How to Safely Use Dapper's IN Clause with Dynamically Generated Values?

Querying with IN Clause Using Dapper ORM

When working with the Dapper ORM, it's common to encounter queries that include an IN clause. However, if the values for the IN clause are dynamically generated from business logic, you might wonder about the best approach to construct such a query.

One method that has been used is string concatenation, but this can become cumbersome and prone to SQL injection vulnerabilities. To avoid these issues, Dapper provides an advanced parameter mapping technique that allows you to specify a parameter for the IN clause.

Solution

Dapper supports the use of a parameter for the IN clause directly. To use this feature, you can follow these steps:

1. Define your query with a placeholder for the IN clause parameter. For example:

string sql = "SELECT * FROM SomeTable WHERE id IN @ids";

2. Create an object that contains the values for the IN clause parameter. In this example, we create an anonymous object with an ids property that contains an array of integer values:

var parameters = new { ids = new[] { 1, 2, 3, 4, 5 } };

3. Execute the query using the Query method and pass in the parameter object as the second argument:

var results = conn.Query(sql, parameters);

This approach is more concise and secure than string concatenation and allows you to easily specify a dynamic list of values for the IN clause.

Note for PostgreSQL Users

If you're using PostgreSQL, the syntax for the IN clause is slightly different. Instead of using a parameter placeholder, you can use the ANY operator to specify the values for the IN clause. For example:

string sql = "SELECT * FROM SomeTable WHERE id = ANY(@ids)";

Just remember to adjust the parameters object accordingly:

var parameters = new { ids = new[] { 1, 2, 3, 4, 5 } };

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