Reflection: method with generic argument and lambda expression as parameter

Question

I really can't figure this one out...

I'm trying to achieve the following result using reflection:

_builder.Entity<Post>().HasKey(p => p.Id);

Let me introduce the variables... _builder is of type DbModelBuilder and Post has a property Id of type Guid.

In the code below, contentType wraps a System.Type :

var config = _builder.GetType()
    .GetMethod("Entity")
    .MakeGenericMethod(contentType.Type)
    .Invoke(_builder, null);

var hasKey = config.GetType().GetMethod("HasKey");

var expressionKey = typeof(Expression<>)
    .MakeGenericType(typeof(Func<,>)
    .MakeGenericType(contentType.Type, typeof(Guid)));

var paramEx = Expression.Parameter(contentType.Type, "t");
var lambdaEx = Expression.Lambda(Expression.Property(paramEx, "Id"), paramEx);

hasKey.MakeGenericMethod(typeof(Guid))
    .Invoke(_builder, new[] { lambdaEx });

HasKey definition might help:

public EntityTypeConfiguration<TEntityType> HasKey<TKey>(Expression<Func<TEntityType, TKey>> keyExpression);

... where TEntityType should be of type Post and TKey of type Guid ...

Exception of type TargetException is thrown (on the last call to Invoke above) :

Object does not match target type.

I have tried every idea I could come up with and still I can't match the target type.

Any help is appreciated.

Not to be blond here, but shouldnt your last invoke's instance parameter be config rather than _builder? :) — Polity
– Polity, Commented Oct 19, 2011 at 3:24
Just curious since i find the idea intriguing. Are you trying to to create some kind of dynamic EF ModelBuilder? — Polity
– Polity, Commented Oct 19, 2011 at 3:28
haha Skeet is still sleeping, allowing me to gain some points ;) — Polity
– Polity, Commented Oct 19, 2011 at 3:28
Yes, this code basically allows you to add Types at runtime and have them persisted in a SQL database, the model checked for database recreation, etc... Dynamic EF ModelBuilder yep! — maxbeaudoin
– maxbeaudoin, Commented Oct 19, 2011 at 3:31
Very interresting, i've been looking at a something similar for a trusted plugin environment and where they can store their data.... Are you planning on making this an opensource project? — Polity
– Polity, Commented Oct 19, 2011 at 3:32

Polity · Accepted Answer · 2011-10-19 03:27:02Z

2

In your last call to Invoke, you specified the wrong instance parameter. Should be 'config' rather than '_builder'

answered Oct 19, 2011 at 3:27

Polity

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maxbeaudoin · Accepted Answer · 2013-12-18 16:33:02Z

0

Silly me, I have no excuses...

How-to Entity Framework & Reflection:

var config = _builder.GetType()
    .GetMethod("Entity")
    .MakeGenericMethod(contentType.Type)
    .Invoke(_builder, null);

var hasKey = config.GetType().GetMethod("HasKey");

var expressionKey = typeof(Expression<>)
    .MakeGenericType(typeof(Func<,>)
    .MakeGenericType(contentType.Type, typeof(Guid)));

var paramEx = Expression.Parameter(contentType.Type, "t");
var lambdaEx = Expression.Lambda(Expression.Property(paramEx, "Id"), paramEx);

hasKey.MakeGenericMethod(typeof(Guid))
    .Invoke(config, new[] { lambdaEx });

edited Dec 18, 2013 at 16:33

answered Oct 19, 2011 at 3:30

maxbeaudoin

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