Question

I created a Generic Repository class like below :

public abstract class Repository<TEntity, TIdentifier> : IRepository<TEntity, TIdentifier> where TEntity : class
{
    //TEntity is type of DBSet and TIdentifier is name of SQL Table's Id column
    protected Repository(DbContext context)
    {
        Context = context;
        DBSet = Context.Set<TEntity>();
    }
}

in this Class we have a method named SelectAll as the following :

[DataObjectMethod(DataObjectMethodType.Select, true)]
public IEnumerable<TEntity> SelectAll(IEnumerable<TIdentifier> ids, List<string> includeNavigationProperties = null)
{
    ParameterExpression parameter = Expression.Parameter(typeof(TEntity), "entity");
    MemberExpression leftParam = Expression.MakeMemberAccess(parameter, typeof(TEntity).GetProperty(IdentifierColumn));
    Expression body = parameter;
    foreach (TIdentifier identifier in ids)
    {
        var rightParam = Expression.Constant(identifier);
        body = Expression.Or(body, Expression.Equal(leftParam, rightParam));//Exception
    }
    return (IEnumerable<TEntity>) DBSet.Select(Expression.Lambda<Func<TEntity, bool>>(body, parameter));
}

As you can see I wanted to select all rows with Id column in IEnumerable<TIdentifier> ids. But the following exception has occurred:

The binary operator Or is not defined for the types ‘DAL.Tag’ and ‘System.Boolean’

Answer 1

If you execute your logic on paper you’ll get something like

1. Expression = Entity
2. Expression = Entity OR (parameter = ids[0]) OR (parameter = ids[1]) …

probably not what you meant unless Entity happens to be a bool.