How do I join 2 tables in ServiceStack OrmLite and select both classes?

Question

I\'d like to do a simple SQL join in ServiceStack OrmLite and get both tables as the corresponding .NET objects.

In LINQ-to-Entities it would be something like this:

Answer 1

This wasn't available in OrmLite previously but as it's a nice feature to have I've just added support for SelectMulti<T,T2,..> and SelectMultiAsync in this commit which now lets you read up to 7 of your joined tables from a single query.

So to use OrmLite's Advanced Join Example you can construct a typed Join Query with:

var q = db.From<Customer>()
    .Join<Customer, CustomerAddress>()
    .Join<Customer, Order>();

Then use the SelectMulti APIs to populate the tables you're interested in, e.g:

var results = db.SelectMulti<Customer, CustomerAddress, Order>(q);

Which will return a List<Tuple<T,T2,T3>> giving you typed access to your populated POCOs from tables in your joined query.

If preferred, there's also an async version:

var results = await db.SelectMultiAsync<Customer, CustomerAddress, Order>(q);

The new SelectMulti APIs are available from v4.0.57 that's now available on MyGet.

Create Typed Queries in OrmLite and Execute them in Dapper

An alternative is to use a combination of OrmLite to create the typed query using its built-in Reference Conventions and then use OrmLite's embedded version of Dapper to Query Multiple result-sets into your existing POCO Types.

To start with create your Typed Query Expression and have it return all fields from all tables with:

var q = db.From<Customer>()
    .Join<Customer, CustomerAddress>()
    .Join<Customer, Order>()
    .Select("*");

Then pass the generated SQL from the above typed SQL Expression into Dapper's Query Multiple feature to read the results into a List of Tuples of the different joined tables:

using (var multi = db.QueryMultiple(q.ToSelectStatement()))
{
    var results = multi.Read<Customer, CustomerAddress, Order, 
        Tuple<Customer,CustomerAddress,Order>>(Tuple.Create).ToList();

    foreach (var tuple in results)
    {
        "Customer:".Print();
        tuple.Item1.PrintDump();

        "Customer Address:".Print();
        tuple.Item2.PrintDump();

        "Order:".Print();
        tuple.Item3.PrintDump();
    }
}

Which prints out something like:

Customer:
{
    Id: 1,
    Name: Customer 1
}
Customer Address:
{
    Id: 1,
    CustomerId: 1,
    AddressLine1: 1 Australia Street,
}
Order:
{
    Id: 1,
    CustomerId: 1,
    LineItem: Line 1,
    Qty: 1,
    Cost: 1.99
}    
Customer:
{
    Id: 1,
    Name: Customer 1
}
Customer Address:
{
    Id: 1,
    CustomerId: 1,
    AddressLine1: 1 Australia Street,
}
Order:
{
    Id: 2,
    CustomerId: 1,
    LineItem: Line 2,
    Qty: 2,
    Cost: 2.99
}