[英]Convert strongly typed Expression to anonymous type return
I'm trying to dynamically convert this type of expression :我正在尝试动态转换这种类型的表达式:
myDbSet.Select(x => new MyClass
{
IsSelected = x.ChildList.Any()
})
into :进入 :
myDbSet.Select(x => new
{
Item = x
IsSelected = x.ChildList.Any()
})
I would write an extension method that would take the strongly typed version and transform into the anonymous then create a new expression in order to do something like this :我会编写一个扩展方法,该方法将采用强类型版本并转换为匿名版本,然后创建一个新表达式以执行以下操作:
myDbSet.Select(anonymousTransformedExpression).ToList().
.Select(newGeneratedExpression)
I would want this newGeneratedExpression to be:我希望这个 newGeneratedExpression 是:
myDbSet.Select(x => new
{
x.Item.IsSelected = x.IsSelected
return x.Item;
})
So basically tranform the return back into a strongly typed but with the "IsSelected" value applied.所以基本上将返回转换回强类型但应用了“IsSelected”值。
Problem is I cant really find a starting point on how to do so..问题是我真的找不到如何做的起点..
EDIT编辑
Alright I realised that the question wasn't so clear and I've come a little closer to the solution with one main problem so far.好吧,我意识到问题不是那么清楚,到目前为止,我已经接近解决一个主要问题的解决方案。 Here's what I got :这是我得到的:
public static IEnumerable<TModel> SelectWithUnmapped<TModel> (this IQueryable<TModel> source, Expression<Func<TModel, object>> assigner) where TModel : class, new()
{
var anonymousType = typeof(AnonymousType<TModel>);
var expression = Expression.New(anonymousType);
var parameter = Expression.Parameter(typeof(TModel), "x");
//this part is hard coded to only take binding at position 0.. eventually will become dynamic
var originalBinding = ((MemberAssignment) ((MemberInitExpression) assigner.Body).Bindings[0]);
var originalExpression = originalBinding.Expression;
Expression conversion = Expression.Convert(originalExpression, typeof(object));
var bindings = new[]
{
Expression.Bind(anonymousType.GetProperty("Item"), parameter),
//this is hardcoded test
Expression.Bind(anonymousType.GetProperty("Property1"), conversion)
};
var body = Expression.MemberInit(expression, bindings);
var lambda = Expression.Lambda<Func<TModel, AnonymousType<TModel>>>(body, parameter);
var test = source.Select(lambda).ToList();
return source;
}
class AnonymousType<TModel>
{
public TModel Item { get; set; }
public object Property1 { get; set; }
public object Property2 { get; set; }
public object Property3 { get; set; }
public object Property4 { get; set; }
public object Property5 { get; set; }
public object Property6 { get; set; }
public object Property7 { get; set; }
public object Property8 { get; set; }
public object Property9 { get; set; }
public object Property10 { get; set; }
public object Property11 { get; set; }
public object Property12 { get; set; }
public object Property13 { get; set; }
public object Property14 { get; set; }
public object Property15 { get; set; }
public object Property16 { get; set; }
public object Property17 { get; set; }
public object Property18 { get; set; }
public object Property19 { get; set; }
public object Property20 { get; set; }
}
}
When I try to assign test, I get the following error : The parameter 'x' was not bound in the specified LINQ to Entities query expression.当我尝试分配测试时,出现以下错误:在指定的 LINQ to Entities 查询表达式中未绑定参数“x”。
This is due to my second binding using the original expression's binding expression.这是由于我使用原始表达式的绑定表达式进行了第二次绑定。 However both use the same parameter name of "x".然而,两者都使用相同的参数名称“x”。 How could I make sure my new binding actually know that x is the parameter from the new expression?我如何确保我的新绑定确实知道 x 是来自新表达式的参数?
So basically so far I'm trying to take in an expression that looks like :所以基本上到目前为止,我正在尝试采用一个看起来像这样的表达式:
x => new Test
{
PropertyTest = x.Blah.Count()
}
into :进入 :
x => new AnonymousType<Test>(){
Item = x,
Property1 = x.Blah.Count()
}
I finally finished it up.我终于完成了。 I guess it just took patience and trial and error a lot.我想这只是需要耐心和反复试验。 To help anyone who would like to do the same.帮助任何想做同样事情的人。 I had to limit myself to a certain property count.. which can be added easily.我不得不将自己限制在特定的财产数量上……这很容易添加。
Here's the code :这是代码:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
public static class IQueryableExtensions
{
public static IEnumerable<TModel> SelectAndAssign<TModel>(this IQueryable<TModel> source, Expression<Func<TModel, object>> assigner) where TModel : class, new()
{
//get typed body of original expression
var originalBody = (MemberInitExpression)assigner.Body;
//list to store the new bindings we're creating for new expression
var newExpressionBindings = new List<MemberBinding>();
var newExpressionReturnType = typeof(AnonymousType<TModel>);
//new param
var parameter = Expression.Parameter(typeof(TModel), "x");
//base binding
newExpressionBindings.Add(Expression.Bind(newExpressionReturnType.GetProperty("Item"), parameter));
//go through all the original expression's bindings
for (var i = 0; i < originalBody.Bindings.Count; i++)
{
var originalBinding = (MemberAssignment)originalBody.Bindings[i];
var originalExpression = originalBinding.Expression;
var memberType = originalBinding.Expression.Type;
//create delegate based on the member type
var originalLambdaDelegate = typeof(Func<,>).MakeGenericType(typeof(TModel), memberType);
//create lambda from that delegate
var originalLambda = Expression.Lambda(originalLambdaDelegate, originalExpression, assigner.Parameters[0]);
//create a AnonymousVar<MemberType> from the type of the member ( to please EF unable to assign bool to object directly )
//start with getting the generic type
var genericMemberType = typeof(AnonymousVar<>).MakeGenericType(memberType);
//then create teh delegate
var genericMemberTypeDelegate = typeof(Func<>).MakeGenericType(genericMemberType);
//Now create an expression with a binding for that object to assign its Property ( strongly typed now from the generic declaration )
var genericInstantiationExpression = Expression.New(genericMemberType);
//the binding.. using the original expression expression
var genericInstantiationBinding = Expression.Bind(genericMemberType.GetProperty("Property"), originalLambda.Body);
// create the body
var genericInstantiationBody = Expression.MemberInit(genericInstantiationExpression, genericInstantiationBinding);
//now we need to recreate a lambda for this
var newBindingExpression = Expression.Lambda(genericMemberTypeDelegate, genericInstantiationBody);
//Create the binding and add it to the new expression bindings
newExpressionBindings.Add(Expression.Bind(newExpressionReturnType.GetProperty("Property" + (i + 1)), newBindingExpression.Body));
}
//start creating the new expression
var expression = Expression.New(newExpressionReturnType);
//create new expression body with bindings
var body = Expression.MemberInit(expression, newExpressionBindings);
//The actual new expression lambda
var newLambda = Expression.Lambda<Func<TModel, AnonymousType<TModel>>>(body, parameter);
// replace old lambda param with new one
var replacer = new ParameterReplacer(assigner.Parameters[0], newLambda.Parameters[0]); // replace old lambda param with new
//new lambda with fixed params
newLambda = Expression.Lambda<Func<TModel, AnonymousType<TModel>>>(replacer.Visit(newLambda.Body), newLambda.Parameters[0]);
//now that we have all we need form the server, we materialize the list
var materialized = source.Select(newLambda).ToList();
//typed return parameter
var typedReturnParameter = Expression.Parameter(typeof(AnonymousType<TModel>), "x");
//Lets assign all those custom properties back into the original object type
var expressionLines = new List<Expression>();
for (var i = 0; i < originalBody.Bindings.Count; i++)
{
var originalBinding = (MemberAssignment)originalBody.Bindings[i];
var itemPropertyExpression = Expression.Property(typedReturnParameter, "Item");
var bindingPropertyExpression = Expression.Property(itemPropertyExpression, originalBinding.Member.Name);
var memberType = originalBinding.Expression.Type;
var valuePropertyExpression = Expression.Convert(Expression.Property(typedReturnParameter, "Property" + (i + 1)), typeof(AnonymousVar<>).MakeGenericType(memberType));
var memberValuePropertyExpression = Expression.Property(valuePropertyExpression, "Property");
var equalExpression = Expression.Assign(bindingPropertyExpression, memberValuePropertyExpression);
expressionLines.Add(equalExpression);
}
var returnTarget = Expression.Label(typeof(TModel));
expressionLines.Add(Expression.Return(returnTarget, Expression.Property(typedReturnParameter, "Item")));
expressionLines.Add(Expression.Label(returnTarget, Expression.Constant(null, typeof(TModel))));
var finalExpression = Expression.Block(expressionLines);
var typedReturnLambda = Expression.Lambda<Func<AnonymousType<TModel>, TModel>>(finalExpression, typedReturnParameter).Compile();
return materialized.Select(typedReturnLambda);
}
class AnonymousVar<TModel>
{
public TModel Property { get; set; }
}
class AnonymousType<TModel>
{
public TModel Item { get; set; }
public object Property1 { get; set; }
public object Property2 { get; set; }
public object Property3 { get; set; }
public object Property4 { get; set; }
public object Property5 { get; set; }
public object Property6 { get; set; }
public object Property7 { get; set; }
public object Property8 { get; set; }
public object Property9 { get; set; }
public object Property10 { get; set; }
public object Property11 { get; set; }
public object Property12 { get; set; }
public object Property13 { get; set; }
public object Property14 { get; set; }
public object Property15 { get; set; }
public object Property16 { get; set; }
public object Property17 { get; set; }
public object Property18 { get; set; }
public object Property19 { get; set; }
public object Property20 { get; set; }
}
class ParameterReplacer : ExpressionVisitor
{
private ParameterExpression from;
private ParameterExpression to;
public ParameterReplacer(ParameterExpression from, ParameterExpression to)
{
this.from = from;
this.to = to;
}
protected override Expression VisitParameter(ParameterExpression node)
{
return base.VisitParameter(node == this.from ? this.to : node);
}
}
}
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