An extended query field class that is being used to define a functional query expression for the SQL statement. This class is very useful if you wish to customize your query expression in many ways. It inherits the QueryField object.

Below is a sample code that is using the TRIM function of the underlying database.

var where = new FunctionalQueryField("Column", "Value", "TRIM({0})");
var result = connection.Query<Entity>(where);

The result would contain all the records where the trimmed value of the Column is equals to Value.

The GetString() method returns a command text that utilizes the passed formatted function.

var where = new FunctionalQueryField("Column", "Value", "TRIM({0})");
var text = where.GetString(connection.GetDbSetting()); // Returns (TRIM([Column]) = @Column)

It is important to take note that the library is using the string.Format() method to compose the formatting of the expression. Therefore, in the format argument of the constructor, always put the {0} format indexer as a placement of the actual field.

See the complex formatting below.

var where = new FunctionalQueryField("Column", "Value", "LEN({0}) > 5 AND RIGHT({0})");
var text = where.GetString(connection.GetDbSetting()); // Returns (LEN([Column]) > 5 AND RIGHT([Column]) = @Column)