How to convert T to object

Question

I am getting error to convert T to Entity

public T Add(T entity)
{
    CAFMEntities db = new CAFMEntities();
    db.TabMasters.AddObject((TabMaster)entity);
    db.SaveChanges();
    return entity;
}

It is giving me an error:

Cannot convert type 'T' to 'CAFM.Data.EntityModel.TabMaster'

Thanks.

Solution

Well, how do you want the conversion to apply? Where is T declared? You may be able to change it so that you have:

class WhateverClass<T> where T : TabMaster

at which point you don't need the cast. Or if you can't constrain T, you can use:

db.TabMasters.AddObject((TabMaster)(object) entity);

An alternative is:

db.TabMasters.AddObject(entity as TabMaster);

although personally I'm not as fond of that - I prefer the stricter checking of the cast.

Comments

[Jon Skeet]

@abatishchev: Apparently so, although of course then you don't get as good checking. Will add that in as an option.

[Admin]

@abatischev Not with your post as is: as only works with reference types, but T is not constrained as such ... now if where T : class (or otherwise constrained to another reference type), then yes.

[Jon Skeet]

@pst: Nope, you don't need to constrain T in order to use as. I've just tried it.

[Admin]

@Jon Skeet void x<T>() { return null as T; } void Main () { x<string>(); } gets me "The type parameter 'T' cannot be used with the 'as' operator because it does not have a class type constraint nor a 'class' constraint" in LINQPad4.

[Admin]

Well, duh. TabMaster is simply a reference type. Underwhelming explanation.

[Jon Skeet]

@pst: That's trying to convert to T - the OP is trying to convert from T. I'm not sure where your last comment is aimed...