CODEWITHSUNDEEP
c#asp.netgenericsinterface
Joe
Joe

Reputation: 735

Convert List<IInfrastructureEntity> to List<TEntity> where generic type TEntity necessarily implements that interface

I have a static class DataSource that pulls requested data from a file and returns it as a List<IInfrastructureEntity>. In TestRepository (below), I am taking the generic TEntity, determining its class type and pulling the corresponding data from DataSource Or, trying to, at least. Instead, I get the following compile-time error on each return statement. Even though anyTEntity necessarily implements IInfrastructureEntity.

Cannot implicitly convert type 'System.Collections.Generic.List<IInfrastructureEntity>' to 'System.Collections.Generic.List<TEntity>'

How do I explicitly make that conversion?

public class TestRepository<TEntity> : IRepository<TEntity> where TEntity : IInfrastructureEntity
{
    public List<TEntity> GetData()
    {
        TEntity checkType = default(TEntity);
        if (checkType is Member) return DataSource.Members;
        if (checkType is MenuItem) return DataSource.MenuItems;
        if (checkType is CRAWApplication) return DataSource.CRAWApplications;
        if (checkType is CRAWEntitlement) return DataSource.CRAWEntitlements;
        if (checkType is FOXGroup) return DataSource.FOXGroups;

        throw new NotSupportedException( checkType.ToString() + " is not yet supported");
    }

    public List<TEntity> FindBy(Expression<Func<TEntity, bool>> predicate)
    {
        return GetData().AsQueryable().Where(predicate);
    }

}

Upvotes: 2

Views: 196

Answers (1)

Christos
Christos

Reputation: 53958

You could fix this by imposing an explicit cast in each list your return:

if (checkType is Member) return DataSource.Members.Cast<TEntity>().ToList();

The problem is that the type of DataSource.Members is List<IInfrastructureEntity>, whereas the type that is expected to be returned is a List<TEntity>. Indeed each Entity should implement IInfrastructureEntity as you have stated this as where TEntity : IInfrastructureEntity. However even if a type implements this interface it doesn't mean that this type can be converted implicitly to TEntity object. This is why you need the explicit cast.

Upvotes: 2

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