Question

I have a class that needs a property set inside a LINQ-to-SQL query. My first attempt was to have a “setter” method that would return the object instance and could be used in my select, like this:

public partial class Foo
{
    public DateTime RetrievalTime { get; set; }

    public Foo SetRetrievalTimeAndReturnSelf ( DateTime value )
    {
        RetrievalTime = value;
        return this;
    }
}

....

from foo in DataContext.GetTable<Foo> select foo.SetRetrievalTimeAndReturnSelf();

Unfortunately, such a query throws an exception like this: “System.NotSupportedException: Method ‘Foo.SetRetrievalTime(System.DateTime)’ has no supported translation to SQL”.

Is there any alternative to converting the result to a list and iterating over it? The query is used in a custom “Get” method that wraps the DataContext.GetTable method, so will be used as the base for many other queries. Immediately converting a potentially-large result set to a list would not be optimal.

UPDATE

Here’s a better example of what I’m trying to do, updated with Jason’s proposed solution:

protected IQueryable<T> Get<T>() where T : class, ISecurable
{
    // retrieve all T records and associated security records
    var query = from entity in DataContext.GetTable<T> ()
                from userEntityAccess in DataContext.GetTable<UserEntityAccess> ()
                where userEntityAccess.SysUserId == CurrentUser.Id
                    && entity.Id == userEntityAccess.EntityId
                    && userEntityAccess.EntityClassName == typeof ( T ).Name
                select new { entity, userEntityAccess };

    return query.AsEnumerable ()
        .Select ( item =>
        {
            item.entity.CanRead = item.userEntityAccess.CanRead;
            item.entity.CanWrite = item.userEntityAccess.CanWrite;
            item.entity.CanDelete = item.userEntityAccess.CanDelete;
            return item.entity;
        } ).AsQueryable ();
}

public interface ISecurable
{
    int Id { get; set; }
    bool CanRead { get; set; }
    bool CanWrite { get; set; }
    bool CanDelete { get; set; }
}

UserEntityAccess is a cross-reference table between a user and a business object record (i.e. an entity). Each record contains fields like “CanRead”, “CanWrite”, and “CanDelete”, and determines what a specific user can do with a specific record.

ISecurable is a marker interface that must be implemented by any LINQ-to-SQL domain class that needs to use this secured Get method.

Answer 1

var projection = DataContext.GetTable<Foo>
                            .AsEnumerable()
                            .Select(f => f.SetRetrievalTimeAndReturnSelf());

This will then perform the invocation of SetRetrievalTimeAndReturnSelf for each instance of Foo in DataContext.GetTable<Foo> when the IEnumerable<Foo> projection is iterated over.

What do you need to know the time that object was yanked of the database for? That’s potentially smelly.