I am creating an application with MVC4 and entity framework 5. How do can I implement this?
I have looked around and found that I need to override SaveChanges .
Does anyone have any sample code on this? I am using code first approach.
As an example, the way I am saving data is as follows,
public class AuditZoneRepository : IAuditZoneRepository
{
private AISDbContext context = new AISDbContext();
public int Save(AuditZone model, ModelStateDictionary modelState)
{
if (model.Id == 0)
{
context.AuditZones.Add(model);
}
else
{
var recordToUpdate = context.AuditZones.FirstOrDefault(x => x.Id == model.Id);
if (recordToUpdate != null)
{
recordToUpdate.Description = model.Description;
recordToUpdate.Valid = model.Valid;
recordToUpdate.ModifiedDate = DateTime.Now;
}
}
try
{
context.SaveChanges();
return 1;
}
catch (Exception ex)
{
modelState.AddModelError("", "Database error has occured. Please try again later");
return -1;
}
}
}
There is no need to override SaveChanges.
You can
Trigger Context.ChangeTracker.DetectChanges(); // may be necessary depending on your Proxy approach
Then analyze the context BEFORE save.
you can then... add the Change Log to the CURRENT Unit of work.
So the log gets saved in one COMMIT transaction.
Or process it as you see fit.
But saving your change log at same time. makes sure it is ONE Transaction.
Analyzing the context sample:
I have a simple tool, to Dump context content to debug output so when in debugger I can use immediate window to check content. eg
You can use this as a starter to prepare your CHANGE Log.
Try it in debugger immediate window. I have FULL dump on my Context class.
Sample Immediate window call. UoW.Context.FullDump();
public void FullDump()
{
Debug.WriteLine("=====Begin of Context Dump=======");
var dbsetList = this.ChangeTracker.Entries();
foreach (var dbEntityEntry in dbsetList)
{
Debug.WriteLine(dbEntityEntry.Entity.GetType().Name + " => " + dbEntityEntry.State);
switch (dbEntityEntry.State)
{
case EntityState.Detached:
case EntityState.Unchanged:
case EntityState.Added:
case EntityState.Modified:
WriteCurrentValues(dbEntityEntry);
break;
case EntityState.Deleted:
WriteOriginalValues(dbEntityEntry);
break;
default:
throw new ArgumentOutOfRangeException();
}
Debug.WriteLine("==========End of Entity======");
}
Debug.WriteLine("==========End of Context======");
}
private static void WriteCurrentValues(DbEntityEntry dbEntityEntry)
{
foreach (var cv in dbEntityEntry.CurrentValues.PropertyNames)
{
Debug.WriteLine(cv + "=" + dbEntityEntry.CurrentValues[cv]);
}
}
private static void WriteOriginalValues(DbEntityEntry dbEntityEntry)
{
foreach (var cv in dbEntityEntry.OriginalValues.PropertyNames)
{
Debug.WriteLine(cv + "=" + dbEntityEntry.OriginalValues[cv]);
}
}
}
EDIT: Get the changes
I use this routine to get chnages...
public class ObjectPair {
public string Key { get; set; }
public object Original { get; set; }
public object Current { get; set; }
}
public virtual IList<ObjectPair> GetChanges(object poco) {
var changes = new List<ObjectPair>();
var thePoco = (TPoco) poco;
foreach (var propName in Entry(thePoco).CurrentValues.PropertyNames) {
var curr = Entry(thePoco).CurrentValues[propName];
var orig = Entry(thePoco).OriginalValues[propName];
if (curr != null && orig != null) {
if (curr.Equals(orig)) {
continue;
}
}
if (curr == null && orig == null) {
continue;
}
var aChangePair = new ObjectPair {Key = propName, Current = curr, Original = orig};
changes.Add(aChangePair);
}
return changes;
}
edit 2 If you must use the Internal Object tracking.
var context = ???// YOUR DBCONTEXT class
// get objectcontext from dbcontext...
var objectContext = ((IObjectContextAdapter) context).ObjectContext;
// for each tracked entry
foreach (var dbEntityEntry in context.ChangeTracker.Entries()) {
//get the state entry from the statemanager per changed object
var stateEntry = objectContext.ObjectStateManager.GetObjectStateEntry(dbEntityEntry.Entity);
var modProps = stateEntry.GetModifiedProperties();
Debug.WriteLine(modProps.ToString());
}
I decompiled EF6 . Get modified is indeed using private bit array to track fields that have
been changed.
// EF decompiled source..... _modifiedFields is a bitarray
public override IEnumerable<string> GetModifiedProperties()
{
this.ValidateState();
if (EntityState.Modified == this.State && this._modifiedFields != null)
{
for (int i = 0; i < this._modifiedFields.Length; ++i)
{
if (this._modifiedFields[i])
yield return this.GetCLayerName(i, this._cacheTypeMetadata);
}
}
}
I want to develop an Eclipse plug-in which get all visible variables for a specific method.
For example:
public class testVariable {
String test1;
Object test2;
void method_test1(){
int test3,test4;
}
void method_test2(){
int test5,test6;
//get variable here!!!!
}
}
I just want to get visible variable is: test1, test2,test5,test6 in method method_test2. What can I do?
Actually, JDT can be used outside of a plug-in, i.e., it can be used in a stand-alone Java application.
The following code can return the variables you want:
public static void parse(char[] str) {
ASTParser parser = ASTParser.newParser(AST.JLS3);
parser.setSource(str);
parser.setKind(ASTParser.K_COMPILATION_UNIT);
final CompilationUnit cu = (CompilationUnit) parser.createAST(null);
cu.accept(new ASTVisitor() {
public boolean visit(VariableDeclarationFragment var) {
System.out.println("variable: " + var.getName());
return false;
}
public boolean visit(MethodDeclaration md) {
if (md.getName().toString().equals("method_test2")) {
md.accept(new ASTVisitor() {
public boolean visit(VariableDeclarationFragment fd) {
System.out.println("in method: " + fd);
return false;
}
});
}
return false;
}
});
}
The output is:
variable: test1
variable: test2
in method: test5
in method: test6
Check out more examples at JDT tutorials.
Considering this IronPython script
def SensorEvent(d):
print d
print d.Message
... how do I access properties of d?
First line of the SensorEvent method successfully prints
{ Message = blah blubb }
however second line throws an exception:
'<>f_anonymousType[str]' object has no attribute 'Message'
Explanation
d is an instance of an anonymous type provided by an invoke from a C# method. I'm invoking it like this:
public static async void ExecutePyFunc(string name, dynamic data)
{
try
{
var f = strategyScope.GetVariable<Action<object>>(name);
if (f != null)
{
await Task.Run(() => f((object)data));
}
}
catch (Exception x)
{
StaticLog("[Callback Exception] Fehler beim Ausführen einer Python Funktion: {0}", x.Message);
}
}
d is a dictionary. Access it like so:
d['Message']
My solution using DynamicObject: I've introduced a class that converts an anonymous type into a known type by copying its properties via reflection (I don't need anything but the properties but it could probably be enhanced for use with fields, methods, functions as well).
Here's what I've come up with:
public class IronPythonKnownType : DynamicObject
{
public IronPythonKnownType(dynamic obj)
{
var properties = obj.GetType().GetProperties();
foreach (PropertyInfo prop in properties)
{
var val = prop.GetValue(obj);
this.Set(prop.Name, val);
}
}
private Dictionary<string, object> _dict = new Dictionary<string, object>();
public override bool TryGetMember(GetMemberBinder binder, out object result)
{
if (_dict.ContainsKey(binder.Name))
{
result = _dict[binder.Name];
return true;
}
return base.TryGetMember(binder, out result);
}
private void Set(string name, object value)
{
_dict[name] = value;
}
public override bool TrySetMember(SetMemberBinder binder, object value)
{
_dict[binder.Name] = value;
return true;
}
}
which effectively converts the anonymous object into something IronPython can handle.
Now I can do that:
def Blubb(a):
print a.Message
without getting the mentioned exception.
I'm wanting to have a simple duck typing example in C# using dynamic objects. It would seem to me, that a dynamic object should have HasValue/HasProperty/HasMethod methods with a single string parameter for the name of the value, property, or method you are looking for before trying to run against it. I'm trying to avoid try/catch blocks, and deeper reflection if possible. It just seems to be a common practice for duck typing in dynamic languages (JS, Ruby, Python etc.) that is to test for a property/method before trying to use it, then falling back to a default, or throwing a controlled exception. The example below is basically what I want to accomplish.
If the methods described above don't exist, does anyone have premade extension methods for dynamic that will do this?
Example: In JavaScript I can test for a method on an object fairly easily.
//JavaScript
function quack(duck) {
if (duck && typeof duck.quack === "function") {
return duck.quack();
}
return null; //nothing to return, not a duck
}
How would I do the same in C#?
//C# 4
dynamic Quack(dynamic duck)
{
//how do I test that the duck is not null,
//and has a quack method?
//if it doesn't quack, return null
}
If you have control over all of the object types that you will be using dynamically, another option would be to force them to inherit from a subclass of the DynamicObject class that is tailored to not fail when a method that does not exist is invoked:
A quick and dirty version would look like this:
public class DynamicAnimal : DynamicObject
{
public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result)
{
bool success = base.TryInvokeMember(binder, args, out result);
// If the method didn't exist, ensure the result is null
if (!success) result = null;
// Always return true to avoid Exceptions being raised
return true;
}
}
You could then do the following:
public class Duck : DynamicAnimal
{
public string Quack()
{
return "QUACK!";
}
}
public class Cow : DynamicAnimal
{
public string Moo()
{
return "Mooooo!";
}
}
class Program
{
static void Main(string[] args)
{
var duck = new Duck();
var cow = new Cow();
Console.WriteLine("Can a duck quack?");
Console.WriteLine(DoQuack(duck));
Console.WriteLine("Can a cow quack?");
Console.WriteLine(DoQuack(cow));
Console.ReadKey();
}
public static string DoQuack(dynamic animal)
{
string result = animal.Quack();
return result ?? "... silence ...";
}
}
And your output would be:
Can a duck quack?
QUACK!
Can a cow quack?
... silence ...
Edit: I should note that this is the tip of the iceberg if you are able to use this approach and build on DynamicObject. You could write methods like bool HasMember(string memberName) if you so desired.
Try this:
using System.Linq;
using System.Reflection;
//...
public dynamic Quack(dynamic duck, int i)
{
Object obj = duck as Object;
if (duck != null)
{
//check if object has method Quack()
MethodInfo method = obj.GetType().GetMethods().
FirstOrDefault(x => x.Name == "Quack");
//if yes
if (method != null)
{
//invoke and return value
return method.Invoke((object)duck, null);
}
}
return null;
}
Or this (uses only dynamic):
public static dynamic Quack(dynamic duck)
{
try
{
//invoke and return value
return duck.Quack();
}
//thrown if method call failed
catch (RuntimeBinderException)
{
return null;
}
}
Implementation of the HasProperty method for every IDynamicMetaObjectProvider WITHOUT throwing RuntimeBinderException.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Dynamic;
using Microsoft.CSharp.RuntimeBinder;
using System.Linq.Expressions;
using System.Runtime.CompilerServices;
namespace DynamicCheckPropertyExistence
{
class Program
{
static void Main(string[] args)
{
dynamic testDynamicObject = new ExpandoObject();
testDynamicObject.Name = "Testovaci vlastnost";
Console.WriteLine(HasProperty(testDynamicObject, "Name"));
Console.WriteLine(HasProperty(testDynamicObject, "Id"));
Console.ReadLine();
}
private static bool HasProperty(IDynamicMetaObjectProvider dynamicProvider, string name)
{
var defaultBinder = Binder.GetMember(CSharpBinderFlags.None, name, typeof(Program),
new[]
{
CSharpArgumentInfo.Create(
CSharpArgumentInfoFlags.None, null)
}) as GetMemberBinder;
var callSite = CallSite<Func<CallSite, object, object>>.Create(new NoThrowGetBinderMember(name, false, defaultBinder));
var result = callSite.Target(callSite, dynamicProvider);
if (Object.ReferenceEquals(result, NoThrowExpressionVisitor.DUMMY_RESULT))
{
return false;
}
return true;
}
}
class NoThrowGetBinderMember : GetMemberBinder
{
private GetMemberBinder m_innerBinder;
public NoThrowGetBinderMember(string name, bool ignoreCase, GetMemberBinder innerBinder) : base(name, ignoreCase)
{
m_innerBinder = innerBinder;
}
public override DynamicMetaObject FallbackGetMember(DynamicMetaObject target, DynamicMetaObject errorSuggestion)
{
var retMetaObject = m_innerBinder.Bind(target, new DynamicMetaObject[] {});
var noThrowVisitor = new NoThrowExpressionVisitor();
var resultExpression = noThrowVisitor.Visit(retMetaObject.Expression);
var finalMetaObject = new DynamicMetaObject(resultExpression, retMetaObject.Restrictions);
return finalMetaObject;
}
}
class NoThrowExpressionVisitor : ExpressionVisitor
{
public static readonly object DUMMY_RESULT = new DummyBindingResult();
public NoThrowExpressionVisitor()
{
}
protected override Expression VisitConditional(ConditionalExpression node)
{
if (node.IfFalse.NodeType != ExpressionType.Throw)
{
return base.VisitConditional(node);
}
Expression<Func<Object>> dummyFalseResult = () => DUMMY_RESULT;
var invokeDummyFalseResult = Expression.Invoke(dummyFalseResult, null);
return Expression.Condition(node.Test, node.IfTrue, invokeDummyFalseResult);
}
private class DummyBindingResult {}
}
}
impromptu-interface seems to be a nice Interface mapper for dynamic objects... It's a bit more work than I was hoping for, but seems to be the cleanest implementation of the examples presented... Keeping Simon's answer as correct, since it is still the closest to what I wanted, but the Impromptu interface methods are really nice.
The shortest path would be to invoke it, and handle the exception if the method does not exist. I come from Python where such method is common in duck-typing, but I don't know if it is widely used in C#4...
I haven't tested myself since I don't have VC 2010 on my machine
dynamic Quack(dynamic duck)
{
try
{
return duck.Quack();
}
catch (RuntimeBinderException)
{ return null; }
}
Have not see a correct answer here, MS provides an example now with casting to a dictionary
dynamic employee = new ExpandoObject();
employee.Name = "John Smith";
employee.Age = 33;
foreach (var property in (IDictionary<String, Object>)employee)
{
Console.WriteLine(property.Key + ": " + property.Value);
}
// This code example produces the following output:
// Name: John Smith
// Age: 33
I have a native C++ dll and two classes:
classA
{
void setNumber(int number);
int getNumber();
}
classB
{
void setclassA(classA*);
classA* getclassA();
}
I have an ATL dll that wraps the native C++ dll and two interfaces: InterfaceForClassA , InterfaceForClassB .
InterfaceForClassA :
STDMETHODIMP CInterfaceForClassA::createClassAObject(void)
{
ClassA* Aobject = new ClassA();
return S_OK;
}
STDMETHODIMP CInterfaceForClassA::setNumberInClassA(SHORT pVal)
{
if(Aobject != NULL)
Aobject->setNumber(pVal);
return S_OK;
}
STDMETHODIMP CInterfaceForClassA::getNumberInClassA(SHORT* pVal)
{
if(Aobject != NULL)
*pVal = Aobject->getNumber();
return S_OK;
}
InterfaceForClassB :
IInterfaceForClassA* clsAInterface;
STDMETHODIMP CInterfaceForClassB::setClassA(IInterfaceForClassA * val)
{
val->QueryInterface(IID_IInterfaceForClassA,(void**)clsAInterface;
}
STDMETHODIMP CInterfaceForClassB::getClassA(IInterfaceForClassA ** returnVal)
{
clsAInterface->QueryInterface(IID_IInterfaceForClassA,(void**)returnVal);
}
and finally i have a c# project that includes the ATL dll, in the c# project i call ATL dll classes:
InterfaceForClassA clsa1 = new InterfaceForClassA();
clsa1.createClassAObject();
clsa1.setNumberInClassA(12);
InterfaceForClassB clsb = new InterfaceForClassB();
clsb.setClassA(clsa1);
InterfaceForClassA clsa2 = new InterfaceForClassA();
clsa2 = clsb.getClassA();
Console.WriteLine("number: " + clsa2.getNumberInClassA());
and when i run the c# project, it gives NullReferenceException error in the last line above. Can you help me?
Your CInterfaceForClassB::setClassA implementation is incorrect. It should be (note the &):
STDMETHODIMP CInterfaceForClassB::setClassA(IInterfaceForClassA * val)
{
val->QueryInterface(IID_IInterfaceForClassA,(void**)&clsAInterface);
}