How Does Dapper's `splitOn` Parameter Handle Multimapping and Column Order?

Multimapping in Dapper: Understanding the SplitOn Parameter

Multimapping in Dapper allows fetching multiple types from a single query. However, users often encounter issues when working with the splitOn parameter.

In the example provided, a ProductItem class with an associated Customer class is being queried. The issue arises when attempting to split the columns into the correct objects. By default, Dapper assumes the split point is the Id column.

Therefore, for the provided code to function correctly, splitOn: "CustomerId,CustomerName" is required. This specifies the starting point for the Customer object.

However, it's important to note that the order of columns in the underlying table is crucial. If the column order changes (e.g., CustomerName comes before CustomerId), using splitOn: "CustomerId" will result in a null customer name.

In such scenarios, using multiple comma-separated split points (e.g., splitOn: "CustomerId,CustomerName") would be necessary to correctly split the result set. This allows Dapper to know that the Customer object starts at the first column and ends at the second column.

Remember, the order of the split points corresponds to the order of the classes in the Dapper query. Understanding this behavior is essential for effectively using multimapping in Dapper.

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