Execute Dynamic Entity in Database using Dapper - asp.net

Question

My user send dynamic entity from client-project so, I have to write methods like this
public Task<TUser> FindByNameAsync(string normalizedUserName, CancellationToken cancellationToken)
{
cancellationToken.ThrowIfCancellationRequested();
throw new NotImplementedException();
//string sql = "SELECT * FROM \"IdentityUsers\" WHERE \"NormalizedUserName\" = #NormalizedUserName;";
//using (var connection = _databaseConnectionFactory.CreateConnectionAsync())
//{
// connection.QueryFirstOrDefaultAsync<TUser>(sql,
// new { NormalizedUserName = normalizedUserName });
//}
}
My IDatabaseConnectionFactory class bind ConnectionString like below:
public interface IDatabaseConnectionFactory
{
Task<IDbConnection> CreateConnectionAsync();
}
public class ConnectionFactory : IDatabaseConnectionFactory
{
private readonly string _connectionString;
public ConnectionFactory(string connectionString) => _connectionString = connectionString ?? throw new ArgumentNullException(nameof(connectionString));
public async Task<IDbConnection> CreateConnectionAsync()
{
try
{
var connString = new NpgsqlConnection(_connectionString);
await connString.OpenAsync();
return connString;
}
catch
{
throw;
}
}
}
Now, how can I execute following query using generic-type entity TUser
string sql = "SELECT * FROM \"IdentityUsers\" WHERE \"NormalizedUserName\" = #NormalizedUserName;";
using (var connection = _databaseConnectionFactory.CreateConnectionAsync())
{
connection.QueryFirstOrDefaultAsync<TUser>(sql,
new { NormalizedUserName = normalizedUserName });
}
Note: QueryFirstOrDefaultAsync not found under connection here

Answer 1

You aren't awaiting the CreateConnectionAsync. Unfortunately it isn't obvious in this case, because Task<T> is disposable (so the using doesn't complain); try instead:
using (var connection = await _databaseConnectionFactory.CreateConnectionAsync())
{
var user = await connection.QueryFirstOrDefaultAsync<TUser>(sql,
new { NormalizedUserName = normalizedUserName });
}
As a tip: the compiler output (against the original code) helps make this clear:
Error CS1929 'Task<IDbConnection>' does not contain a definition for 'QueryFirstOrDefaultAsync' and the best extension method overload 'SqlMapper.QueryFirstOrDefaultAsync<TUser>(IDbConnection, string, object, IDbTransaction, int?, CommandType?)' requires a receiver of type 'IDbConnection'
which tells us that:
it found some QueryFirstOrDefaultAsync method, but it wasn't usable, because
the target expression is a Task<IDbConnection>, not an IDbConnection
As a side note: it is worth knowing that if you're only doing one operation with the connection, Dapper can deal with opening and closing the connection for you - which can help reduce the number of async/await operations. Consider, for example, if you had a CreateClosedConnection() method that did not open the connection, and thus had no need to be async; the following would still work:
using (var connection = _databaseConnectionFactory.CreateClosedConnection())
{
var user = await connection.QueryFirstOrDefaultAsync<TUser>(sql,
new { NormalizedUserName = normalizedUserName });
}
with Dapper dealing with the await OpenAsync() for you as part of the QueryFirstOrDefaultAsync.