I would like to replace the default SystemTextJsonInputFormatter with a custom input formatter, either as a sub-class of TextInputFormatter, or (preferably) SystemTextJsonInputFormatter; preferably the latter, to be as close as possible to the built-in ASp.NET Core behaviour without having to duplicate code into my class, which would need to be periodically updated as new ASP.NET Core releases make changes to SystemTextJsonInputFormatter.
There is some relevant info here:
Custom formatters in ASP.NET Core Web API
Which provide this example of how to register a custom input formatter:
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers(options =>
{
options.InputFormatters.Insert(0, new VcardInputFormatter());
});
However, I currently also have this customisation of the JSON options, like so:
internal static IServiceCollection ConfigureJsonSerialization(this IServiceCollection services)
{
services.AddControllers().AddJsonOptions(opts => {
// Note. some of these settings are defaults, but we ensure they are set as required.
opts.JsonSerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull;
opts.JsonSerializerOptions.PropertyNameCaseInsensitive = false;
opts.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;
// Add our custom converters.
opts.JsonSerializerOptions.Converters.Add(new DateOnlyJsonConverter());
});
return services;
}
opts there is a Microsoft.AspNetCore.Mvc.JsonOptions object.
When using the built-in SystemTextJsonInputFormatter, these options make it into that formatter instance via its constructor (the relevant code appears to be in MvcCoreMvcOptionsSetup).
I would like to use those same JSON options in my custom input formatter, but cannot see how to obtain a JsonOptions at construction time (the options.InputFormatters.Insert(0, new VcardInputFormatter()); line from above.
I will continue to look through ASP.NET Core internals to try and figure out a way, but thought I would ask here in case anyone can offer some guidance.
Thanks.
A somewhat hacky approach is to simply copy the JsonSerializerOptions properties from the existing SystemTextJsonInputFormatter instance provided by ASP.NET Core, like so:
public static class ServiceCollectionExtensions
{
internal static IServiceCollection ConfigureJsonSerialization(this IServiceCollection services)
{
services.AddControllers(
opts => {
// Search for an existing instance of SystemTextJsonInputFormatter in the InputFormatters list;
// this is the instance provided as standard by ASP.NET Core.
int idx = FindSystemTextJsonInputFormatter(
opts.InputFormatters,
out SystemTextJsonInputFormatter? sysTextJsonInputFormatter);
// We expect to find the SystemTextJsonInputFormatter.
if (sysTextJsonInputFormatter is null)
throw new InvalidOperationException("No SystemTextJsonInputFormatter is defined.");
// We will now create our own input formatter, and swap it in to substitute the
// SystemTextJsonInputFormatter instance. First we have some objects to setup.
// Copy the json serializer settings from the existing SystemTextJsonInputFormatter.
var jsonOptions = new JsonOptions();
CopyJsonSerializerOptions(
jsonOptions.JsonSerializerOptions,
sysTextJsonInputFormatter.SerializerOptions);
// TODO/FIXME: Research how best to get a logger for our input formatter!
var loggerFactory = LoggerFactory.Create(builder => {
builder.AddConsole();
});
var logger = loggerFactory.CreateLogger<SystemTextJsonInputFormatter>();
// Perform the substitution.
opts.InputFormatters[idx] = new JsonMergePatchInputFormatter(jsonOptions, logger);
})
.AddJsonOptions(opts => {
// Note. some of these settings are defaults, but we ensure they are set as required.
opts.JsonSerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull;
opts.JsonSerializerOptions.PropertyNameCaseInsensitive = false;
opts.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;
// Add our custom converters.
opts.JsonSerializerOptions.Converters.Add(new DateOnlyJsonConverter());
});
return services;
}
private static int FindSystemTextJsonInputFormatter(
FormatterCollection<IInputFormatter> inputFormatters,
out SystemTextJsonInputFormatter? sysTextJsonInputFormatter)
{
// Search for an instance of SystemTextJsonInputFormatter, and store it's index in the InputFormatters list.
// Note. We expect only one instance at most, but if there is more then one then we simply take the first instance.
for (int i = 0; i < inputFormatters.Count; i++)
{
if (inputFormatters[i] is SystemTextJsonInputFormatter formatter)
{
sysTextJsonInputFormatter = formatter;
return i;
}
}
// Not found.
sysTextJsonInputFormatter = null;
return -1;
}
private static void CopyJsonSerializerOptions(JsonSerializerOptions targetOptions, JsonSerializerOptions sourceOptions)
{
// Notes. A hacky but necessary approach, because we are given a pre-built JsonSerializerOptions object
// that can't be replaced, therefore we must copy the various setting into it.
targetOptions.AllowTrailingCommas = sourceOptions.AllowTrailingCommas;
targetOptions.DefaultBufferSize = sourceOptions.DefaultBufferSize;
targetOptions.DefaultIgnoreCondition = sourceOptions.DefaultIgnoreCondition;
targetOptions.DictionaryKeyPolicy = sourceOptions.DictionaryKeyPolicy;
targetOptions.Encoder = sourceOptions.Encoder;
targetOptions.IgnoreNullValues = sourceOptions.IgnoreNullValues;
targetOptions.IgnoreReadOnlyFields = sourceOptions.IgnoreReadOnlyFields;
targetOptions.IncludeFields = sourceOptions.IncludeFields;
targetOptions.MaxDepth = sourceOptions.MaxDepth;
targetOptions.NumberHandling = sourceOptions.NumberHandling;
targetOptions.PropertyNameCaseInsensitive = sourceOptions.PropertyNameCaseInsensitive;
targetOptions.PropertyNamingPolicy = sourceOptions.PropertyNamingPolicy;
targetOptions.ReadCommentHandling = sourceOptions.ReadCommentHandling;
targetOptions.ReferenceHandler = sourceOptions.ReferenceHandler;
targetOptions.UnknownTypeHandling = sourceOptions.UnknownTypeHandling;
targetOptions.WriteIndented = sourceOptions.WriteIndented;
targetOptions.DefaultIgnoreCondition = sourceOptions.DefaultIgnoreCondition;
targetOptions.DefaultIgnoreCondition = sourceOptions.DefaultIgnoreCondition;
// Re-use the same converter instances; this is OK because their current parent
// SystemTextJsonInputFormatter is about to be discarded.
targetOptions.Converters.Clear();
foreach (var jsonConverter in sourceOptions.Converters)
{
targetOptions.Converters.Add(jsonConverter);
}
}
}
I spent some time wading through ASP.NET Core source code and call stacks in an attempt to find a better/cleaner/official way, but ultimately had to give up and go with the above. Please do let me know if there are better solutions.
I have a hierarchy of actors in Akka.Net and am wondering whether I've chosen the right way to do something, or if there are better/simpler ways to achieve what I want.
My specific example is that I'm constructing a User actor in response to a user logging into the system, and when constructing this actor there are two pieces of data I need in order to complete the construction of the actor.
If this were regular .NET code I might have something like the following...
public Task<User> LoadUserAsync (string username)
{
IProfileService profileService = ...;
IMessageService messageService = ...;
var loadProfileTask = profileService.GetUserProfileAsync(username);
var loadMessagesTask = messageService.GetMessagesAsync(username);
Task.WaitAll(loadProfileTask, loadMessagesTask);
// Now construct the user from the result of both tasks
var user = new User
{
Profile = loadProfileTask.Result,
Messages = loadMessagesTask.Result
}
return Task.FromResult(user);
}
Here I use WaitAll to wait for the subordinate tasks to complete, and let them run concurrently.
My question is - if I wanted to do the same in Akka.Net, would the following be the most regular way to do this? Pictorially I've created the following...
When I create my User actor, I then construct a (temporary) User Loader Actor, whose job it is to get the full user details by calling to the Profile actor and the Messages actor. The leaf actors that get the data are as follows...
public class UserProfileLoader : ReceiveActor
{
public UserProfileLoader()
{
Receive<LoadUserRequest>(msg =>
{
// Load the user profile from somewhere
var profile = new UserProfile();
// And respond to the Sender
Sender.Tell(profile);
Self.Tell(PoisonPill.Instance);
});
}
}
public class UserMessagesLoader : ReceiveActor
{
public UserMessagesLoader()
{
Receive<LoadUserRequest>(msg =>
{
// Load the messages from somewhere
var messages = new List<Message>();
// And respond to the Sender
Sender.Tell(messages);
Self.Tell(PoisonPill.Instance);
});
}
}
It doesn't really matter where they get the data from for this discussion, but both simply respond to a request by returning some data.
Then I have the actor that coordinates the two data gathering actors...
public class UserLoaderActor : ReceiveActor
{
public UserLoaderActor()
{
Receive<LoadUserRequest>(msg => LoadProfileAndMessages(msg));
Receive<UserProfile>(msg =>
{
_profile = msg;
FinishIfPossible();
});
Receive<List<Message>>(msg =>
{
_messages = msg;
FinishIfPossible();
});
}
private void LoadProfileAndMessages(LoadUserRequest msg)
{
_originalSender = Sender;
Context.ActorOf<UserProfileLoader>().Tell(msg);
Context.ActorOf<UserMessagesLoader>().Tell(msg);
}
private void FinishIfPossible()
{
if ((null != _messages) && (null != _profile))
{
_originalSender.Tell(new LoadUserResponse(_profile, _messages));
Self.Tell(PoisonPill.Instance);
}
}
private IActorRef _originalSender;
private UserProfile _profile;
private List<Message> _messages;
}
This just creates the two subordinate actors, sends them a message to get cracking, and then waits for both to respond before sending back all the data that's been gathered to the original requestor.
So, does this seem like a reasonable way to coordinate two disparate responses, in order to combine them? Is there an easier way to do this than craft it up myself?
Thanks in advance for your responses!
Thanks folks, so I've now simplified the actor significantly into the following, based on both Roger and Jeff's suggestions...
public class TaskBasedUserLoader : ReceiveActor
{
public TaskBasedUserLoader()
{
Receive<LoadUserRequest>(msg => LoadProfileAndMessages(msg));
}
private void LoadProfileAndMessages(LoadUserRequest msg)
{
var originalSender = Sender;
var loadPreferences = this.LoadProfile(msg.UserId);
var loadMessages = this.LoadMessages(msg.UserId);
Task.WhenAll(loadPreferences, loadMessages)
.ContinueWith(t => new UserLoadedResponse(loadPreferences.Result, loadMessages.Result),
TaskContinuationOptions.AttachedToParent & TaskContinuationOptions.ExecuteSynchronously)
.PipeTo(originalSender);
}
private Task<UserProfile> LoadProfile(string userId)
{
return Task.FromResult(new UserProfile { UserId = userId });
}
private Task<List<Message>> LoadMessages(string userId)
{
return Task.FromResult(new List<Message>());
}
}
The LoadProfile and LoadMessages methods will ultimately call a repository to get the data, but for now I have a succinct way to do what I wanted.
Thanks again!
IMHO that's a valid process, as you fork action and then join it.
BTW you could use this.Self.GracefulStop(new TimeSpan(1)); instead of sending poison pill.
You could use a combination of Ask, WhenAll and PipeTo:
var task1 = actor1.Ask<Result1>(request1);
var task2 = actor2.Ask<Result2>(request2);
Task.WhenAll(task1, task2)
.ContinueWith(_ => new Result3(task1.Result, task2.Result))
.PipeTo(Self);
...
Receive<Result3>(msg => { ... });
Just came across the latest build of Mono.CSharp and love the promise it offers.
Was able to get the following all worked out:
namespace XAct.Spikes.Duo
{
class Program
{
static void Main(string[] args)
{
CompilerSettings compilerSettings = new CompilerSettings();
compilerSettings.LoadDefaultReferences = true;
Report report = new Report(new Mono.CSharp.ConsoleReportPrinter());
Mono.CSharp.Evaluator e;
e= new Evaluator(compilerSettings, report);
//IMPORTANT:This has to be put before you include references to any assemblies
//our you;ll get a stream of errors:
e.Run("using System;");
//IMPORTANT:You have to reference the assemblies your code references...
//...including this one:
e.Run("using XAct.Spikes.Duo;");
//Go crazy -- although that takes time:
//foreach (Assembly assembly in AppDomain.CurrentDomain.GetAssemblies())
//{
// e.ReferenceAssembly(assembly);
//}
//More appropriate in most cases:
e.ReferenceAssembly((typeof(A).Assembly));
//Exception due to no semicolon
//e.Run("var a = 1+3");
//Doesn't set anything:
//e.Run("a = 1+3;");
//Works:
//e.ReferenceAssembly(typeof(A).Assembly);
e.Run("var a = 1+3;");
e.Run("A x = new A{Name=\"Joe\"};");
var a = e.Evaluate("a;");
var x = e.Evaluate("x;");
//Not extremely useful:
string check = e.GetVars();
//Note that you have to type it:
Console.WriteLine(((A) x).Name);
e = new Evaluator(compilerSettings, report);
var b = e.Evaluate("a;");
}
}
public class A
{
public string Name { get; set; }
}
}
And that was fun...can create a variable in the script's scope, and export the value.
There's just one last thing to figure out... how can I get a value in (eg, a domain entity that I want to apply a Rule script on), without using a static (am thinking of using this in a web app)?
I've seen the use compiled delegates -- but that was for the previous version of Mono.CSharp, and it doesn't seem to work any longer.
Anybody have a suggestion on how to do this with the current version?
Thanks very much.
References:
* Injecting a variable into the Mono.CSharp.Evaluator (runtime compiling a LINQ query from string)
* http://naveensrinivasan.com/tag/mono/
I know it's almost 9 years later, but I think I found a viable solution to inject local variables. It is using a static variable but can still be used by multiple evaluators without collision.
You can use a static Dictionary<string, object> which holds the reference to be injected. Let's say we are doing all this from within our class CsharpConsole:
public class CsharpConsole {
public static Dictionary<string, object> InjectionRepository {get; set; } = new Dictionary<string, object>();
}
The idea is to temporarily place the value in there with a GUID as key so there won't be any conflict between multiple evaluator instances. To inject do this:
public void InjectLocal(string name, object value, string type=null) {
var id = Guid.NewGuid().ToString();
InjectionRepository[id] = value;
type = type ?? value.GetType().FullName;
// note for generic or nested types value.GetType().FullName won't return a compilable type string, so you have to set the type parameter manually
var success = _evaluator.Run($"var {name} = ({type})MyNamespace.CsharpConsole.InjectionRepository[\"{id}\"];");
// clean it up to avoid memory leak
InjectionRepository.Remove(id);
}
Also for accessing local variables there is a workaround using Reflection so you can have a nice [] accessor with get and set:
public object this[string variable]
{
get
{
FieldInfo fieldInfo = typeof(Evaluator).GetField("fields", BindingFlags.NonPublic | BindingFlags.Instance);
if (fieldInfo != null)
{
var fields = fieldInfo.GetValue(_evaluator) as Dictionary<string, Tuple<FieldSpec, FieldInfo>>;
if (fields != null)
{
if (fields.TryGetValue(variable, out var tuple) && tuple != null)
{
var value = tuple.Item2.GetValue(_evaluator);
return value;
}
}
}
return null;
}
set
{
InjectLocal(variable, value);
}
}
Using this trick, you can even inject delegates and functions that your evaluated code can call from within the script. For instance, I inject a print function which my code can call to ouput something to the gui console window:
public delegate void PrintFunc(params object[] o);
public void puts(params object[] o)
{
// call the OnPrint event to redirect the output to gui console
if (OnPrint!=null)
OnPrint(string.Join("", o.Select(x => (x ?? "null").ToString() + "\n").ToArray()));
}
This puts function can now be easily injected like this:
InjectLocal("puts", (PrintFunc)puts, "CsInterpreter2.PrintFunc");
And just be called from within your scripts:
puts(new object[] { "hello", "world!" });
Note, there is also a native function print but it directly writes to STDOUT and redirecting individual output from multiple console windows is not possible.
Here's the table
Users
UserId
UserName
Password
EmailAddress
and the code..
public void ChangePassword(int userId, string password){
//code to update the password..
}
Ladislav's answer updated to use DbContext (introduced in EF 4.1):
public void ChangePassword(int userId, string password)
{
var user = new User() { Id = userId, Password = password };
using (var db = new MyEfContextName())
{
db.Users.Attach(user);
db.Entry(user).Property(x => x.Password).IsModified = true;
db.SaveChanges();
}
}
You can tell entity-framework which properties have to be updated in this way:
public void ChangePassword(int userId, string password)
{
var user = new User { Id = userId, Password = password };
using (var context = new ObjectContext(ConnectionString))
{
var users = context.CreateObjectSet<User>();
users.Attach(user);
context.ObjectStateManager.GetObjectStateEntry(user)
.SetModifiedProperty("Password");
context.SaveChanges();
}
}
In Entity Framework Core, Attach returns the entry, so all you need is:
var user = new User { Id = userId, Password = password };
db.Users.Attach(user).Property(x => x.Password).IsModified = true;
db.SaveChanges();
You have basically two options:
go the EF way all the way, in that case, you would
load the object based on the userId provided - the entire object gets loaded
update the password field
save the object back using the context's .SaveChanges() method
In this case, it's up to EF how to handle this in detail. I just tested this, and in the case I only change a single field of an object, what EF creates is pretty much what you'd create manually, too - something like:
`UPDATE dbo.Users SET Password = #Password WHERE UserId = #UserId`
So EF is smart enough to figure out what columns have indeed changed, and it will create a T-SQL statement to handle just those updates that are in fact necessary.
you define a stored procedure that does exactly what you need, in T-SQL code (just update the Password column for the given UserId and nothing else - basically executes UPDATE dbo.Users SET Password = #Password WHERE UserId = #UserId) and you create a function import for that stored procedure in your EF model and you call this function instead of doing the steps outlined above
i'm using this:
entity:
public class Thing
{
[Key]
public int Id { get; set; }
public string Info { get; set; }
public string OtherStuff { get; set; }
}
dbcontext:
public class MyDataContext : DbContext
{
public DbSet<Thing > Things { get; set; }
}
accessor code:
MyDataContext ctx = new MyDataContext();
// FIRST create a blank object
Thing thing = ctx.Things.Create();
// SECOND set the ID
thing.Id = id;
// THIRD attach the thing (id is not marked as modified)
db.Things.Attach(thing);
// FOURTH set the fields you want updated.
thing.OtherStuff = "only want this field updated.";
// FIFTH save that thing
db.SaveChanges();
While searching for a solution to this problem, I found a variation on GONeale's answer through Patrick Desjardins' blog:
public int Update(T entity, Expression<Func<T, object>>[] properties)
{
DatabaseContext.Entry(entity).State = EntityState.Unchanged;
foreach (var property in properties)
{
var propertyName = ExpressionHelper.GetExpressionText(property);
DatabaseContext.Entry(entity).Property(propertyName).IsModified = true;
}
return DatabaseContext.SaveChangesWithoutValidation();
}
"As you can see, it takes as its second parameter an expression of a
function. This will let use this method by specifying in a Lambda
expression which property to update."
...Update(Model, d=>d.Name);
//or
...Update(Model, d=>d.Name, d=>d.SecondProperty, d=>d.AndSoOn);
( A somewhat similar solution is also given here: https://stackoverflow.com/a/5749469/2115384 )
The method I am currently using in my own code, extended to handle also (Linq) Expressions of type ExpressionType.Convert. This was necessary in my case, for example with Guid and other object properties. Those were 'wrapped' in a Convert() and therefore not handled by System.Web.Mvc.ExpressionHelper.GetExpressionText.
public int Update(T entity, Expression<Func<T, object>>[] properties)
{
DbEntityEntry<T> entry = dataContext.Entry(entity);
entry.State = EntityState.Unchanged;
foreach (var property in properties)
{
string propertyName = "";
Expression bodyExpression = property.Body;
if (bodyExpression.NodeType == ExpressionType.Convert && bodyExpression is UnaryExpression)
{
Expression operand = ((UnaryExpression)property.Body).Operand;
propertyName = ((MemberExpression)operand).Member.Name;
}
else
{
propertyName = System.Web.Mvc.ExpressionHelper.GetExpressionText(property);
}
entry.Property(propertyName).IsModified = true;
}
dataContext.Configuration.ValidateOnSaveEnabled = false;
return dataContext.SaveChanges();
}
New EF Core 7 native feature — ExecuteUpdate:
Finally! After a long wait, EF Core 7.0 now has a natively supported way to run UPDATE (and also DELETE) statements while also allowing you to use arbitrary LINQ queries (.Where(u => ...)), without having to first retrieve the relevant entities from the database: The new built-in method called ExecuteUpdate — see "What's new in EF Core 7.0?".
ExecuteUpdate is precisely meant for these kinds of scenarios, it can operate on any IQueryable instance, and lets you update specific columns on any number of rows, while always issuing a single UPDATE statement behind the scenes, making it as efficient as possible.
Usage:
Let's take OP's example — i.e. updating the password column of a specific user:
dbContext.Users
.Where(u => u.Id == someId)
.ExecuteUpdate(b =>
b.SetProperty(u => u.Password, "NewPassword")
);
As you can see, calling ExecuteUpdate requires you to make calls to the SetProperty method, to specify which property to update, and also what new value to assign to it.
EF Core will translate this into the following UPDATE statement:
UPDATE [u]
SET [u].[Password] = "NewPassword"
FROM [Users] AS [u]
WHERE [u].[Id] = someId
Also, ExecuteDelete for deleting rows:
There's also a counterpart to ExecuteUpdate called ExecuteDelete, which, as the name implies, can be used to delete a single or multiple rows at once without having to first fetch them.
Usage:
// Delete users that haven't been active in 2022:
dbContext.Users
.Where(u => u.LastActiveAt.Year < 2022)
.ExecuteDelete();
Similar to ExecuteUpdate, ExecuteDelete will generate DELETE SQL statements behind the scenes — in this case, the following one:
DELETE FROM [u]
FROM [Users] AS [u]
WHERE DATEPART(year, [u].[LastActiveAt]) < 2022
Other notes:
Keep in mind that both ExecuteUpdate and ExecuteDelete are "terminating", meaning that the update/delete operation will take place as soon as you call the method. You're not supposed to call dbContext.SaveChanges() afterwards.
If you're curious about the SetProperty method, and you're confused as to why ExectueUpdate doesn't instead receive a member initialization expression (e.g. .ExecuteUpdate(new User { Email = "..." }), then refer to this comment (and the surrounding ones) on the GitHub issue for this feature.
Furthermore, if you're curious about the rationale behind the naming, and why the prefix Execute was picked (there were also other candidates), refer to this comment, and the preceding (rather long) conversation.
Both methods also have async equivalents, named ExecuteUpdateAsync, and ExecuteDeleteAsync respectively.
In EntityFramework Core 2.x there is no need for Attach:
// get a tracked entity
var entity = context.User.Find(userId);
entity.someProp = someValue;
// other property changes might come here
context.SaveChanges();
Tried this in SQL Server and profiling it:
exec sp_executesql N'SET NOCOUNT ON;
UPDATE [User] SET [someProp] = #p0
WHERE [UserId] = #p1;
SELECT ##ROWCOUNT;
',N'#p1 int,#p0 bit',#p1=1223424,#p0=1
Find ensures that already loaded entities do not trigger a SELECT and also automatically attaches the entity if needed (from the docs):
Finds an entity with the given primary key values. If an entity with the given primary key values is being tracked by the context, then it is returned immediately without making a request to the database. Otherwise, a query is made to the database for an entity with the given primary key values and this entity, if found, is attached to the context and returned. If no entity is found, then null is returned.
I'm late to the game here, but this is how I am doing it, I spent a while hunting for a solution I was satisified with; this produces an UPDATE statement ONLY for the fields that are changed, as you explicitly define what they are through a "white list" concept which is more secure to prevent web form injection anyway.
An excerpt from my ISession data repository:
public bool Update<T>(T item, params string[] changedPropertyNames) where T
: class, new()
{
_context.Set<T>().Attach(item);
foreach (var propertyName in changedPropertyNames)
{
// If we can't find the property, this line wil throw an exception,
//which is good as we want to know about it
_context.Entry(item).Property(propertyName).IsModified = true;
}
return true;
}
This could be wrapped in a try..catch if you so wished, but I personally like my caller to know about the exceptions in this scenario.
It would be called in something like this fashion (for me, this was via an ASP.NET Web API):
if (!session.Update(franchiseViewModel.Franchise, new[]
{
"Name",
"StartDate"
}))
throw new HttpResponseException(new HttpResponseMessage(HttpStatusCode.NotFound));
Entity framework tracks your changes on objects that you queried from database via DbContext. For example if you DbContext instance name is dbContext
public void ChangePassword(int userId, string password){
var user = dbContext.Users.FirstOrDefault(u=>u.UserId == userId);
user.password = password;
dbContext.SaveChanges();
}
I know this is an old thread but I was also looking for a similar solution and decided to go with the solution #Doku-so provided. I'm commenting to answer the question asked by #Imran Rizvi , I followed #Doku-so link that shows a similar implementation. #Imran Rizvi's question was that he was getting an error using the provided solution 'Cannot convert Lambda expression to Type 'Expression> [] ' because it is not a delegate type'. I wanted to offer a small modification I made to #Doku-so's solution that fixes this error in case anyone else comes across this post and decides to use #Doku-so's solution.
The issue is the second argument in the Update method,
public int Update(T entity, Expression<Func<T, object>>[] properties).
To call this method using the syntax provided...
Update(Model, d=>d.Name, d=>d.SecondProperty, d=>d.AndSoOn);
You must add the 'params' keyword in front of the second arugment as so.
public int Update(T entity, params Expression<Func<T, object>>[] properties)
or if you don't want to change the method signature then to call the Update method you need to add the 'new' keyword, specify the size of the array, then finally use the collection object initializer syntax for each property to update as seen below.
Update(Model, new Expression<Func<T, object>>[3] { d=>d.Name }, { d=>d.SecondProperty }, { d=>d.AndSoOn });
In #Doku-so's example he is specifying an array of Expressions so you must pass the properties to update in an array, because of the array you must also specify the size of the array. To avoid this you could also change the expression argument to use IEnumerable instead of an array.
Here is my implementation of #Doku-so's solution.
public int Update<TEntity>(LcmsEntities dataContext, DbEntityEntry<TEntity> entityEntry, params Expression<Func<TEntity, object>>[] properties)
where TEntity: class
{
entityEntry.State = System.Data.Entity.EntityState.Unchanged;
properties.ToList()
.ForEach((property) =>
{
var propertyName = string.Empty;
var bodyExpression = property.Body;
if (bodyExpression.NodeType == ExpressionType.Convert
&& bodyExpression is UnaryExpression)
{
Expression operand = ((UnaryExpression)property.Body).Operand;
propertyName = ((MemberExpression)operand).Member.Name;
}
else
{
propertyName = System.Web.Mvc.ExpressionHelper.GetExpressionText(property);
}
entityEntry.Property(propertyName).IsModified = true;
});
dataContext.Configuration.ValidateOnSaveEnabled = false;
return dataContext.SaveChanges();
}
Usage:
this.Update<Contact>(context, context.Entry(modifiedContact), c => c.Active, c => c.ContactTypeId);
#Doku-so provided a cool approach using generic's, I used the concept to solve my issue but you just can't use #Doku-so's solution as is and in both this post and the linked post no one answered the usage error questions.
Combining several suggestions I propose the following:
async Task<bool> UpdateDbEntryAsync<T>(T entity, params Expression<Func<T, object>>[] properties) where T : class
{
try
{
var entry = db.Entry(entity);
db.Set<T>().Attach(entity);
foreach (var property in properties)
entry.Property(property).IsModified = true;
await db.SaveChangesAsync();
return true;
}
catch (Exception ex)
{
System.Diagnostics.Debug.WriteLine("UpdateDbEntryAsync exception: " + ex.Message);
return false;
}
}
called by
UpdateDbEntryAsync(dbc, d => d.Property1);//, d => d.Property2, d => d.Property3, etc. etc.);
Or by
await UpdateDbEntryAsync(dbc, d => d.Property1);
Or by
bool b = UpdateDbEntryAsync(dbc, d => d.Property1).Result;
I use ValueInjecter nuget to inject Binding Model into database Entity using following:
public async Task<IHttpActionResult> Add(CustomBindingModel model)
{
var entity= await db.MyEntities.FindAsync(model.Id);
if (entity== null) return NotFound();
entity.InjectFrom<NoNullsInjection>(model);
await db.SaveChangesAsync();
return Ok();
}
Notice the usage of custom convention that doesn't update Properties if they're null from server.
ValueInjecter v3+
public class NoNullsInjection : LoopInjection
{
protected override void SetValue(object source, object target, PropertyInfo sp, PropertyInfo tp)
{
if (sp.GetValue(source) == null) return;
base.SetValue(source, target, sp, tp);
}
}
Usage:
target.InjectFrom<NoNullsInjection>(source);
Value Injecter V2
Lookup this answer
Caveat
You won't know whether the property is intentionally cleared to null OR it just didn't have any value it. In other words, the property value can only be replaced with another value but not cleared.
_context.Users.UpdateProperty(p => p.Id, request.UserId, new UpdateWrapper<User>()
{
Expression = p => p.FcmId,Value = request.FcmId
});
await _context.SaveChangesAsync(cancellationToken);
Update Property is an extension method
public static void UpdateProperty<T, T2>(this DbSet<T> set, Expression<Func<T, T2>> idExpression,
T2 idValue,
params UpdateWrapper<T>[] updateValues)
where T : class, new()
{
var entity = new T();
var attach = set.Attach(entity);
attach.Property(idExpression).IsModified = false;
attach.Property(idExpression).OriginalValue = idValue;
foreach (var update in updateValues)
{
attach.Property(update.Expression).IsModified = true;
attach.Property(update.Expression).CurrentValue = update.Value;
}
}
And Update Wrapper is a class
public class UpdateWrapper<T>
{
public Expression<Func<T, object>> Expression { get; set; }
public object Value { get; set; }
}
I was looking for same and finally I found the solution
using (CString conn = new CString())
{
USER user = conn.USERs.Find(CMN.CurrentUser.ID);
user.PASSWORD = txtPass.Text;
conn.SaveChanges();
}
believe me it work for me like a charm.
public async Task<bool> UpdateDbEntryAsync(TEntity entity, params Expression<Func<TEntity, object>>[] properties)
{
try
{
this.Context.Set<TEntity>().Attach(entity);
EntityEntry<TEntity> entry = this.Context.Entry(entity);
entry.State = EntityState.Modified;
foreach (var property in properties)
entry.Property(property).IsModified = true;
await this.Context.SaveChangesAsync();
return true;
}
catch (Exception ex)
{
throw ex;
}
}
public void ChangePassword(int userId, string password)
{
var user = new User{ Id = userId, Password = password };
using (var db = new DbContextName())
{
db.Entry(user).State = EntityState.Added;
db.SaveChanges();
}
}