Dapper List Parameter Discover How to Execute Where 'IN' Clause

Description

Dapper supports multiple ways to specify list parameters. The simplest is just passing comma-separated values. Dapper allows you to specify multiple parameters on an IN clause by using a list.

• The list parameters are passed as an anonymous type which means that the definition of the object doesn't matter.
• The object is anonymous, you need to give each parameter a unique name.
• This can be done by using the syntax param1, param2, etc., or by giving each property in the object a different name.

For example, let's say we want to pass a list of IDs to a SQL query and we would use that SQL statement in the Query method as shown below.

var ids = new[] { 1, 2, 3 };

var sql = "SELECT * FROM Customers WHERE CustomerID IN @Ids;";

using (var connection = My.ConnectionFactory())
{
	connection.Open();

	var customer = connection.Query<Customer>(sql, new {Ids = ids }).ToList();
}

Notice that we have given the Ids parameter a unique name. It will return all customers that match the above query.

In Dapper, the IN clause is used to specify a list of values to be compared against a column in a WHERE clause. The SQL IN predicate can be used to easily test if an expression matches any value in a list.

For example, let's say we have different kinds of invoices and we want to find all records in our database table that have a value matching either StoreInvoice or WebInvoice. We can use the IN clause to do this as shown in the below example.

var sql = "SELECT * FROM Invoice WHERE Kind IN @Kind;";

using (var connection = My.ConnectionFactory())
{
	connection.Open();

	var invoices = connection.Query<Invoice>(sql, new {Kind = new[] {InvoiceKind.StoreInvoice, InvoiceKind.WebInvoice}}).ToList();
}

In the above example, we are using the @Ids and @Kind parameters to pass in our list of values. Dapper will automatically convert this into a SQL IN clause.

You can also use the Execute method to execute a SQL query that contains an IN clause. This is useful when you want to delete or update multiple records at once. For example, suppose we want to delete a list of customers as shown in the below example.

var ids = new[] { 2, 3, 5 };

var sql = "DELETE FROM Customers WHERE CustomerID IN @Ids";

using (var connection = My.ConnectionFactory())
{
	connection.Open();

	connection.Execute(sql, new { Ids = ids });
}

As you can see, using Dapper's IN clause support is a simple and convenient way to work with lists of values in your SQL queries.