C# implement interface on "where TEntity : class"

Question

I'm relatively new to .NET and I've stumbled on this particular issue: while following a tutorial on repository pattern, the definition of the class goes like this:

public class GenericRepository<TEntity> where TEntity : class { ...

That being said, this class is supposed to implement an interface. Since I already used the : operator, how do I do that?

I tried going public class GenericRepository<TEntity> : IGenericRepository where TEntity : class { and also public class GenericRepository<TEntity> where TEntity : class : IGenericRepository { but it doesnt work

do you mean the generic parameter should implement an interface or the type itself ? — Selman Genç
– Selman Genç, Commented Feb 5, 2015 at 21:57
@Selman22 I assumed the latter ("this class is supposed to implement an interface"), but it's not clear. — Wai Ha Lee
– Wai Ha Lee, Commented Feb 5, 2015 at 22:05

Jon Skeet · Accepted Answer · 2015-02-05 21:55:09Z

5

Since I already used the : operator, how do I do that?

: isn't an operator - you're just using it in the generic type constraint. You can still specify an interface to implement.

This should be fine:

public class GenericRepository<TEntity> : IGenericRepository where TEntity : class

Or if IGenericRepository is a generic interface, you might want:

public class GenericRepository<TEntity> : IGenericRepository<TEntity>
    where TEntity : class

answered Feb 5, 2015 at 21:55

Jon Skeet

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1 Comment

Christopher Francisco Over a year ago

Accepted this answer because the interface is also a generic and it was also confusing how to declare: ... : IGenericRepository<TEntity> where...

Noel · Accepted Answer · 2015-02-05 21:55:31Z

0

Use a comma to add multiple generic constraints:

public class GenericRepository<TEntity> where TEntity : class, IGenericRepository {}

answered Feb 5, 2015 at 21:55

Noel

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Comments

codebased · Accepted Answer · 2015-02-05 21:59:49Z

public class GenericRepository<TEntity> : **IGenericRepository**<TEntity> where TEntity : class

or

In my case all classes are inheriting from IdentityBaseClass thus my signature looks like:

public class GenericRepository<TEntity> : IGenericRepository<TEntity> where TEntity : IdentityBase

Having said that what it mean is my classes, whoever wants to use GenericRepository, must inherit from IdentityBase class.

My IdentityBase class has got two properties.

 public class IdentityBase
    {
        /// <summary>
        /// Gets or sets ID.
        /// </summary>
        [NonNegative]
        [DataMember(IsRequired = true)]
        public int ID
        {
            get;
            set;
        }

        /// <summary>
        /// Gets or sets the unique identifier of a row; this is to do with replication in SQL.
        /// </summary>

        public Guid UniqueIdentifier
       { 
            get;
            set;
        }

Wai Ha Lee · Accepted Answer · 2015-02-05 23:14:55Z

0

You'd say public class GenericRepository<TEntity> : BaseClass1, IInterface1, IInterface2, ... where TEntity : class { ...

The : you used refers to the generic type parameter needing to be a class (rather than a struct), so you can add an additional ":".

edited Feb 5, 2015 at 23:14

answered Feb 5, 2015 at 21:56

Wai Ha Lee

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