Dapper Multi-Type Result Discover How to Map Result to Different Types
Description
One of the features of Dapper is its ability to map columns from a query result to properties of a different type and you can call it a "multi-type" result.
- You can use the
ExecuteReadermethod which can be called from any object of typeIDbConnection. - It can execute a query and map the result to a list of different types.
- It is useful when you want to combine the data from multiple rows into a single object.
- For example, if you have a query that returns a list of store invoices and web invoices, you can use a multi-type result feature to map each kind of invoice to the
Invoiceobject.
The following example shows how to use the ExecuteReader method and get the multi-type result.
string sql = "SELECT * FROM Invoice;"; using (var connection = My.ConnectionFactory()) { connection.Open(); var invoices = new List<Invoice>(); using (var reader = connection.ExecuteReader(sql)) { var storeInvoiceParser = reader.GetRowParser<StoreInvoice>(); var webInvoiceParser = reader.GetRowParser<WebInvoice>(); while (reader.Read()) { Invoice invoice; switch ((InvoiceKind) reader.GetInt32(reader.GetOrdinal("Kind"))) { case InvoiceKind.StoreInvoice: invoice = storeInvoiceParser(reader); break; case InvoiceKind.WebInvoice: invoice = webInvoiceParser(reader); break; default: throw new Exception(ExceptionMessage.GeneralException); } invoices.Add(invoice); } } }
In the above example, both store invoices and web invoices are mapped to the List<Invoice>.
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