Entity Framework and LINQ together Batch Update - sql

Afaik Entity Framework 6 doesn't support for batch insert/update/delete.
Is there anyway to make an batch update over an IQueryable object. As an example I have
var query = _db.People.Where(x=>x.Name.Contains(parameter));
an IQueryable (query) object and I want to get the generated sql. Then I hope I can create an update command with this select query like this
Update filteredPerson
Set filteredPerson.Status = 'Updated'
from (here it comes IQueryable Generated SQL :) ) as filteredPerson
over DbContext raw sql execution commands. BTW I don't need EF properties like change tracking and auto detecting. It is just a batch operation.
I know it is pretty risky but I am going to use it for a small piece of code.
Some other logics are appricated. If you know something better, I would like to hear it.
REASON: Why I want to do it this way, because I don't want to spoil the seperation of layers. And there is some validation and filtering comes into the queryable object from other layers. So it is hard to convert it to stored procedure. At the other hand it must be faster than other standard queries.
Again I know there is no support in Entity Framework 6 for batch operations. But other questions are bit outdated. That's another reason why I want to ask this again.

While I was writing the question, I was guessing how I am going to solve it. But I was looking for some more proper way of it. In the end, I know what am I doing and tried to be simple for my colleagues who looking to the same code after me. I know it has some risky usages but I let the exceptions to CLR to handle it. After this excuse :) , I wrote the code like this:
Let's say I have an IQueryable object which is generated with this way:
string parameter = "John";
AdventureWorks2012Entities _db = new AdventureWorks2012Entities();
var query = _db.People.AsQueryable();
//Some parameters added from different layers
query = query.Where(x => x.FirstName.Contains(parameter));
Then I want a batch update over this IQueryable object.
var sqlFrom = query.ToString(); //This is the query which becomes "from table"
var dbq = query.AsDbQuery().GetObjectQuery(); //This does some magic with reflection
var linqParams = dbq.Parameters
.Select(x => new System.Data.SqlClient.SqlParameter(x.Name, x.Value)).ToList();
linqParams.Add(new System.Data.SqlClient.SqlParameter("#ModDate", DateTime.Now));
var sqlBatchUpdate = #"Update filteredPerson Set ModifiedDate = #ModDate From (#FilteredPerson) as filteredPerson"
.Replace("#FilteredPerson", sqlFrom);
var affectedRows = _db.Database.ExecuteSqlCommand(sqlBatchUpdate, linqParams.ToArray());
That's it! Now I don't have to repeat same business logic in stored procedure again. And it is more faster than a foreach and SaveChanges combo.
So I ended up with this for very basic usage. As a fast solution It brings more problems no doubt! But I know I can easily wrap around it for new purposes. So It is up to programmer who wants to use it with more preferences.
Also the code which does the reflection and casting is below and I added a gist for full code:
public static ObjectQuery<T> GetObjectQuery<T>(this DbQuery<T> query)
{
var internalQueryField = query.GetType()
.GetFields(BindingFlags.NonPublic | BindingFlags.Instance)
.Where(f => f.Name.Equals("_internalQuery"))
.FirstOrDefault();
var internalQuery = internalQueryField.GetValue(query);
var objectQueryField = internalQuery.GetType()
.GetFields(BindingFlags.NonPublic | BindingFlags.Instance)
.Where(f => f.Name.Equals("_objectQuery"))
.FirstOrDefault();
var objectQuery = objectQueryField.GetValue(internalQuery) as ObjectQuery<T>;
return objectQuery;
}
Here is the Gist file. Hope It helps somebody out there.

Related

Using SQL instead of Linq to query database and return Json

I am developing an application using ASP.Net MVC and AngularJS. I am not familiar with linq and honestly I don't like it. But I am very familiar with SQL and I can perform complex queries. So, my question is, I want you to look at the below code from my MVC controller:
public JsonResult GetSupervisor()
{
var db = new scaleDBEntities();
return this.Json((from userObj in db.Users
select new
{
supervisorId = userObj.Id,
supervisorfName = userObj.usrFirstName,
supervisorlName = userObj.usrLastName,
})
, JsonRequestBehavior.AllowGet
);
}
How can I change the link query into SQL query?
I believe that I can do something like this:
var blogNames = db.Database.SqlQuery<string>("SELECT Name FROM dbo.Blogs").ToList();
So, if this is right, how can i use in in my return this.Json() for my angular?
Using the example you provided, something like this should work:
return this.Json(new {blogNames});
You're just creating an anonymously-typed object that the JSON serializer can use to produce an object like this:
{
"blogNames": ["blog one", "blog two"]
}
It'll be more complicated if you're trying to produce more complex results from a more complex query. But, well, that's what an ORM is for. I'd echo Gert Arnold's advice to embrace LINQ, rather than just deciding you don't like it because you're not used to it.

"Convert" Entity Framework program to raw SQL

I used Entity Framework to create a prototype for a project and now that it's working I want to make the program ready for production.
I face many challenges with EF, the biggest one being the concurrency management (it's a financial software).
Given that it seems to have no way to handle pessimistic concurrency with EF, I have to switch to stored procs in SQL.
To be honest I'm a bit afraid of the workload that may represent.
I would like to know if anybody have been in the same situation before and what is the best strategy to convert a .net code using EF to raw SQL.
Edit:
I'm investigating CLR but it's not clear if pessimistic concurency can be manage with it. is it an option more interesting than TSQl in this case ? It would allow me to reuse part of my C# code and structure of function calling another functions, if I understand well.
I was there and the good news is you don't have to give up Entity Framework if you don't want to. The bad news is you have to update the database yourself. Which isn't as hard as it seems. I'm currently using EF 5 but plan to go to EF 6. I don't see why this still wouldn't work for EF 6.
First thing is in the constructor of the DbContext cast it to IObjectContextAdapter and get access to the ObjectContext. I make a property for this
public virtual ObjectContext ObjContext
{
get
{
return ((IObjectContextAdapter)this).ObjectContext;
}
}
Once you have that subscribe to the SavingChanges event - this isn't our exact code some things are copied out of other methods and redone. This just gives you an idea of what you need to do.
ObjContext.SavingChanges += SaveData;
private void SaveData(object sender, EventArgs e)
{
var context = sender as ObjectContext;
if (context != null)
{
context.DetectChanges();
var tsql = new StringBuilder();
var dbParams = new List<KeyValuePair<string, object>>();
var deletedEntites = context.ObjectStateManager.GetObjectStateEntries(EntityState.Deleted);
foreach (var delete in deletedEntites)
{
// Set state to unchanged - so entity framework will ignore
delete.ChangeState(EntityState.Unchanged);
// Method to generate tsql for deleting entities
DeleteData(delete, tsql, dbParams);
}
var addedEntites = context.ObjectStateManager.GetObjectStateEntries(EntityState.Added);
foreach (var add in addedEntites)
{
// Set state to unchanged - so entity framework will ignore
add.ChangeState(EntityState.Unchanged);
// Method to generate tsql for added entities
AddData(add, tsql, dbParams);
}
var editedEntites = context.ObjectStateManager.GetObjectStateEntries(EntityState.Modified);
foreach (var edit in editedEntites)
{
// Method to generate tsql for updating entities
UpdateEditData(edit, tsql, dbParams);
// Set state to unchanged - so entity framework will ignore
edit.ChangeState(EntityState.Unchanged);
}
if (!tsql.ToString().IsEmpty())
{
var dbcommand = Database.Connection.CreateCommand();
dbcommand.CommandText = tsql.ToString();
foreach (var dbParameter in dbParams)
{
var dbparam = dbcommand.CreateParameter();
dbparam.ParameterName = dbParameter.Key;
dbparam.Value = dbParameter.Value;
dbcommand.Parameters.Add(dbparam);
}
var results = dbcommand.ExecuteNonQuery();
}
}
}
Why we set the entity to unmodified after the update because you can do
var changed properties = edit.GetModifiedProperties();
to get a list of all the changed properties. Since all the entities are now marked as unchanged EF will not send any updates to SQL.
You will also need to mess with the metadata to go from entity to table and property to fields. This isn't that hard to do but messing the metadata does take some time to learn. Something I still struggle with sometimes. I refactored all that out into an IMetaDataHelper interface where I pass it in the entity type and property name to get the table and field back - along with caching the result so I don't have to query metadata all the time.
At the end the tsql is a batch that has all the T-SQL how we want it with the locking hints and containing the transaction level. We also change numeric fields from just being set to nfield = 10 but to be nfield = nfield + 2 in the TSQL if the user updated them by 2 to avoid the concurrency issue as well.
What you wont get to is having SQL locked once someone starts to edit your entity but I don't see how you would get that with stored procedures as well.
All in all it took me about 2 solid days to get this all up and running for us.

Linq order by with a field to retrieve dynamically in vb.net

I have a object Ob with several fields f1,..,fn (of different types).
Now a list of object is shown in a GridView and I need to implement the sorting method.
The real problem is:
how can I run
(from ob in Ob_list orderby ob.f1 ascending)
when the sorting field is represented by a string (i.e. "f1")?
Unfortunately I am not able to get it with the reflection (I am not able to do something like ob.GetType().GetField("f1"), this is not mapped into sql code).
I have several fields to possibly sort the rows, which is the best&fastest approach to this?
Thank you very much!
LINQ execution is deferred until you actually enumerate over the results or access the "count", etc. Because of this, you can build up your LINQ statement in stages.
The below code is done in C#, but I'm sure the equivalent is possible in VB.NET.
First setup your basic query:
var query = (from ob in Ob_list);
At this point, nothing has actually gone to the database due to deferred execution.
Next, conditionally add your order by components:
if (sortField == "f1")
{
query = query.OrderBy(o => o.f1);
}
else if (sortField == "f2")
{
query = query.OrderBy(o => o.f2);
}
else
{
//...
}
And finally, collect your results
foreach (var item in query)
{
// Process the item
}
I've found this question: How do I specify the Linq OrderBy argument dynamically?
I'm using Entity Framework, so the first answer did not solved my problem. The second one however, worked great!
Hope it helps!

How to delete data in DB efficiently using LinQ to NHibernate (one-shot-delete)

Producing software for customers, mostly using MS SQL but some Oracle, a decision was made to plunge into Nhibernate (and C#).
The task is to delete efficiently e.g. 10 000 rows from 100 000 and still stay sticked to ORM.
I've tried named queries - link already,
IQuery sql = s.GetNamedQuery("native-delete-car").SetString(0, "Kirsten");
sql.ExecuteUpdate();
but the best I have ever found seems to be:
using (ITransaction tx = _session.BeginTransaction())
{
try
{
string cmd = "delete from Customer where Id < GetSomeId()";
var count = _session.CreateSQLQuery(cmd).ExecuteUpdate();
...
Since it may not get into dB to get all complete rows before deleting them.
My questions are:
If there is a better way for this kind of delete.
If there is a possibility to get the Where condition for Delete like this:
Having a select statement (using LinQ to NHibernate) => which will generate appropriate SQL for DB => we get that Where condition and use it for Delete.
If there is a better way for this kind of delete.
Yes, you could use HQL instead of SQL.
If there is a possibility to get the Where condition for Delete [using Expressions]:
No, AFAIK that's not implemented. Since NHibernate is an open source project, I encourage you to find out if anyone has proposed this, and/or discuss it on the mailing list.
Thanks for your quick reply. Now I've probably got the difference.
session.CreateSQLQuery(cmd).ExecuteUpdate();
must have cmd with Delete From DbTable. On the contrary the HQL way
session.CreateQuery(cmd).ExecuteUpdate();
needs cmd with Delete From MappedCollectionOfObjects.
In that case it possibly solves my other question as well.
There now is a better way with NHibernate 5.0:
var biggestId = GetSomeId();
session.Query<Customer>()
.Where(c => c.Id < biggestId)
.Delete();
Documentation:
//
// Summary:
// Delete all entities selected by the specified query. The delete operation is
// performed in the database without reading the entities out of it.
//
// Parameters:
// source:
// The query matching the entities to delete.
//
// Type parameters:
// TSource:
// The type of the elements of source.
//
// Returns:
// The number of deleted entities.
public static int Delete<TSource>(this IQueryable<TSource> source);

NHibernate Partial Update

Is there a way in NHibernate to start with an unproxied model
var m = new Model() { ID = 1 };
m.Name = "test";
//Model also has .LastName and .Age
Now save this model only updating Name without first selecting the model from the session?
If model has other properties then name, you need to initialize these with the original value in the database, unless they will be set to null.
You can use HQL update operations; I never tried it myself.
You could also use a native SQL statement. ("Update model set name ...").
Usually, this optimization is not needed. There are really rare cases where you need to avoid selecting the data, so writing this SQL statements are just a waste of time. You are using an ORM, this means: write your software object oriented! Unless you won't get much advantages from it.
What Stefan says looks like what you need. Please be aware that this is really an edge case and you should be happy with fully loading your entity unless you have some ultra-high-performance issues.
If you simply don't want to hit the database - try using caching - entity cache is very simple and efficient.
If your entity is a huge one - i.e. it contains a blob or something - think about splitting it in two (with many-to-one so that you can utilize lazy loading).
http://www.hibernate.org/hib_docs/nhibernate/html/mapping.html
dynamic-update (optional, defaults to
false): Specifies that UPDATE SQL
should be generated at runtime and
contain only those columns whose
values have changed.
Place dynamic-update on the class in the HBM.
var m = new Model() { ID = 1 };
m = session.Update(m); //attach m to the session.
m.Name = "test";
session.Save(m);