Create an Expression<Func<,>> using reflection

c#, expression, lambda, moq, reflection

Solution

The code to create the expression dynamically would be like this:

ParameterExpression parameter = Expression.Parameter(typeof (GoalsModelUnitOfWork), "i");
MemberExpression property = Expression.Property(parameter, "AcademicCycles");

var queryableType = typeof (IQueryable<>).MakeGenericType(typeof (AcademicCycle));
var delegateType = typeof (Func<,>).MakeGenericType(typeof (GoalsModelUnitOfWork), queryableType);

var yourExpression = Expression.Lambda(delegateType, property, parameter);

The result will have the desired type, but the problem is that the return type of `Expression.Lambda()` is `LambdaExpression` and you can't perform a type cast to `Expression<Func<...>>` to pass it as parameter to your setup function because you don't know the generic type parameters for the `Func`. So you have to invoke the `Setup` method by reflection, too:

this.GetType().GetMethod("Setup", yourExpression.GetType()).Invoke(this, yourExpression);

Problem

Im using Moq to create mocks of a data set. I have created a little helper class that allows me to have an in memory storage instead of a database that makes unit testing a breeze. That way I can add and remove items from my mock data set, this allows me to test my insert and delete service calls. During the setup of the mock I have a line that looks like the following ``` this.Setup(i => i.AcademicCycles).Returns(mockStore.GetList<AcademicCycle>()); ``` My mock has a lot of properties so I would like to perform this setup step using reflection. I have managed to the `Returns` part of the process working via reflection but I am stuck on the lambda method to `Setup`. `Setup` takes an `Expression<Func<GoalsModelUnitOfWork, IQueryable<AcademicCycle>>>` that corresponds to the `i => i.AcademicCycles` and I would like to create this dynamically. Using reflection I have the following: The name of the property: "AcademicCycles" The type `IQueryable<AcademicCycle>` The type `AcademicCycle` I also have the instance of the `i` in the lambda statement which is a `GoalsModelUnitOfWork`

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