Using Dapper and Postgresql - citext data type

You probably need to create create a CitextParameter which extends ICustomQueryParameter. This API allows you to pass an arbitrary DbParameter instance to Dapper - in this case it would be an instance of NpgsqlParameter with its NpgsqlDbType set to Citext.

Something like this should work:

class CitextParameter : SqlMapper.ICustomQueryParameter{    readonly string _value;    public CitextParameter(string value)    {        _value = value;    }    public void AddParameter(IDbCommand command, string name)    {        command.Parameters.Add(new NpgsqlParameter        {            ParameterName = name,            NpgsqlDbType = NpgsqlDbType.Citext,            Value = _value        });    }}

When you write the SQL query, you can cast the parameter value like cast(@param as citext).

in my case below worked correctly. (usr is a class object)

string sql = "select * from users where user_name = cast(@user_name as citext) and password = @password;";IEnumerable<users> u = cnn.Query<users>(sql, usr);

In your case, you can change the query like below and see if that works

string sql = @"select * from ""dbo"".""MyFunction""(cast(@schemaName as citext), cast(@tableName as citext));";