具有通用 ID 的通用存储库 - 如何在 int 时检索

Question

I have a generic repository that is the base class for all repositories in my project. The repository has generic support for the primary key, so it's not necessarily an int .

My initial implementation was this, to retrieve an object by ID:

return Context.Set<TDomainObject>().Where(x => x.Id.Equals(id)).SingleOrDefaultAsync();

Where Id is type TPrimaryKey . When I attempt to use this logic for an int , I get a NotSupportedException with the message

Unable to create a constant value of type 'System.Object'. Only primitive types or enumeration types are supported in this context`.

So I thought I'd be clever, and special case where TPrimaryKey is int and do the evaluation like so:

if (typeof(TPrimaryKey) == typeof(int))
{
    int iId = (int)(object)id;
    return Context.Set<TDomainObject>().Where(x => ((int)(object)x.Id) == iId).SingleOrDefaultAsync();
}

This yields a different exception:

Unable to cast the type 'System.Int32' to type 'System.Object'. LINQ to Entities only supports casting EDM primitive or enumeration types.`

How can I make my generic repository work with ints?

Answer 1

您可以使用Find方法

return Context.Set<TDomainObject>().Find(id);