Dynamic Select EntityFramework and System.Linq.Dynamic

问题

Im using the DynamicQueryable.Select() // dynamic select library

The only docu I have found so far is System.Linq.Dynamic docu

I have this query with anonymous return type which works.

var result = Context.Set<TPocoText>().Where((Expression<Func<TPocoText, bool>>) whereLambda)
                     .OrderByDescending(t => t.RowVersion).Skip(skip).Take(take)
                     .Select("new (m1,m2,Nav1) ");

and this works like select(t=> new {t.m1,t.m2,t.Nav1}) as expected

my Question How can it do the equivalent of select(t=> new {t,t.Nav1})

i tried .Select("new (it,Nav1) ") and .Select("new (this,Nav1) ")

the result was a parse error member not found. Anybody know this dynamic string parsing API?

OR the equivalent Expression building syntax is also an option.

NOTE:The Nav Property ForSourceRecord is only known at runtime otherwise i would just use the normal lambda expression.

回答1:

This cannot be done using anon types. The compiler just doesn't have the information needed to work, especially with the free text/string approach.

Try this...

var param = System.Linq.Expressions.Expression.Parameter(typeof(TPocoText));
var init = System.Linq.Expressions.Expression.MemberInit(
    System.Linq.Expressions.Expression.New(typeof(Foo)),
    new []{
        System.Linq.Expressions.Expression.Bind(GetMemberInfo((Foo f) => f.Nav), System.Linq.Expressions.Expression.PropertyOrField(param, "NameOfPropertyToBindToNav")),
        System.Linq.Expressions.Expression.Bind(GetMemberInfo((Foo f) => f.M1), System.Linq.Expressions.Expression.PropertyOrField(param, "M1")),
    }
);
var result = Context.Set<TPocoText>().Where((Expression<Func<TPocoText, bool>>) whereLambda)
                 .OrderByDescending(t => t.RowVersion).Skip(skip).Take(take)
                 .Select(System.Linq.Expressions.Expression.Lambda<Func<TPocoText, Foo>>(init, param));



public class Foo
{
    public string Nav {get;set;}
    public string M1 {get;set;}
}
public static MemberInfo GetMemberInfo<T, U>(Expression<Func<T, U>> expression)
{
    var member = expression.Body as MemberExpression;
    if (member != null)
        return member.Member;

    throw new ArgumentException("Expression is not a member access", "expression");
}

来源：https://stackoverflow.com/questions/17333325/dynamic-select-entityframework-and-system-linq-dynamic

标签

entity-framework

lambda