Correct use of multimapping in Dapper

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I just ran a test that works fine: 

var sql = "select cast(1 as decimal) ProductId, 'a' ProductName, 'x' AccountOpened, cast(1 as decimal) CustomerId, 'name' CustomerName";

var item = connection.Query<ProductItem, Customer, ProductItem>(sql,
    (p, c) => { p.Customer = c; return p; }, splitOn: "CustomerId").First();

item.Customer.CustomerId.IsEqualTo(1);

The splitOn param needs to be specified as the split point, it defaults to Id. If there are multiple split points, you will need to add them in a comma delimited list.

Say your recordset looks like this: 

ProductID | ProductName | AccountOpened | CustomerId | CustomerName 
---------------------------------------   -------------------------

Dapper needs to know how to split the columns in this order into 2 objects. A cursory look shows that the Customer starts at the column CustomerId, hence splitOn: CustomerId.

There is a big caveat here, if the column ordering in the underlying table is flipped for some reason:

ProductID | ProductName | AccountOpened | CustomerName | CustomerId  
---------------------------------------   -------------------------

splitOn: CustomerId will result in a null customer name.

If you specify CustomerId,CustomerName as split points, dapper assumes you are trying to split up the result set into 3 objects. First starts at the beginning, second starts at CustomerId, third at CustomerName.

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