getting an error on trying to call method in generic way

问题

Hi all I am trying to filter the table using where class by passing parameter to the method like as below,

    private IQueryable<SpaceFunctionType> Get<TEntity>(Expression<Func<TEntity, bool>> predicate) where TEntity : class, ICategorySpaceFunction
    {
        return _dbContext.Set<TEntity>().Where(predicate)
                              .Select(c => new SpaceFunctionType
                              {
                                  Category = c.Category,
                                  SpaceFunction = c.SpaceFunction
                              });
    }

   public IQueryable<SpaceFunctionType> GetSpaceFunctionType(string environmentSource)
   {
        return Get<LibraryEnvironment>(x => x.EnvironmentSource.Name == environmentSource).AsQueryable();
   }

and these are the interface details,

public interface ICategorySpaceFunction
{
    public string Category { get; set; }
    public string SpaceFunction { get; set; }
}

and this will be the class name

public class SpaceFunctionType : ICategorySpaceFunction
{
    public string Category { get; set; }
    public string SpaceFunction { get; set; }
}

but getting an error here Get<LibraryEnvironment> like as below

The type 'API.DesignHub.Entities.LibraryEnvironment' cannot be used as type parameter 'TEntity' in the generic type or method 'Query.Get(Expression>)'. There is no implicit reference conversion from 'API.DesignHub.Entities.LibraryEnvironment' to 'API.DesignHub.Entities.ICategorySpaceFunction'

I am not sure where i am doing wrong with the above method, Could any one please suggest any idea on this that would be very grateful to me,

Many thanks in advance

回答1:

The error is what it is happening. But the language used there is a bit generic. What it means is LibraryEnvironment does not implement ICategorySpaceFunction. TEntity is a type of ICategorySpaceFunction and you are sending LibraryEnvironment when calling, so it is a rule that LibraryEnvironment should be similar to TEntity, which is an implementation of ICategorySpaceFunction. more details - https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/generics/constraints-on-type-parameters

来源：https://stackoverflow.com/questions/59868996/getting-an-error-on-trying-to-call-method-in-generic-way

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