How to Correctly Use Dapper's Multimapping with Multiple Customer Columns?

Correct Use of Multimapping in Dapper

Dapper's multimapping feature allows retrieving multiple types from a single query. In the example provided, the goal is to return a list of products and their associated customers.

The sample Dapper code defines two classes: ProductItem and Customer. The query successfully returns products and their customers, but the "splitOn" parameter must include the complete customer column list to retrieve all customer properties.

The misunderstanding lies in the interpretation of the "splitOn" parameter. It specifies the point at which the columns should be split into multiple objects. By default, it splits at the Id property. However, in this case, the customer properties start at the "CustomerId" column.

To correct the issue, the "splitOn" parameter should be modified to:

splitOn: "CustomerId"

This will result in the correct mapping, where the "Customer" property of each ProductItem instance will contain the associated customer data.

It's important to note that the column order in the underlying table is crucial. If the order of the customer columns is changed, the "splitOn" parameter will need to be adjusted accordingly to maintain accurate mapping.

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