当数组参数的值为 null 时无法确定其类型

Question

使用 PostgreSQL 数据库和 Dapper。

这是失败代码的一个最小示例：

await using var connection = new NpgsqlConnection(_configuration.ConnectionString);

return await connection.QueryAsync<Diamond>(
  @"SELECT
      id,
      name
    FROM
      product
    WHERE
      @Names IS NULL OR name = ANY(@Names);",
  new
  {
      Names = Names,
  });

如果 Names = new { "Tom", "Dick", "Harry" }.

这会很好用

但是如果 Names = (string[]) null.

它会失败

我得到的错误是：

Npgsql.PostgresException (0x80004005): 42P18: could not determine data type of parameter 
   at Npgsql.NpgsqlConnector.<>c__DisplayClass160_0.<<DoReadMessage>g__ReadMessageLong|0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Npgsql.NpgsqlConnector.<>c__DisplayClass160_0.<<DoReadMessage>g__ReadMessageLong|0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Npgsql.NpgsqlDataReader.NextResult(Boolean async, Boolean isConsuming)
   at Npgsql.NpgsqlCommand.ExecuteReaderAsync(CommandBehavior behavior, Boolean async, CancellationToken cancellationToken)
   at Npgsql.NpgsqlCommand.ExecuteDbDataReaderAsync(CommandBehavior behavior, CancellationToken cancellationToken)
   at Dapper.SqlMapper.QueryAsync[T](IDbConnection cnn, Type effectiveType, CommandDefinition command) in /_/Dapper/SqlMapper.Async.cs:line 419

是否可以将 Dapper 中的可为空数组参数发送到 PostgreSQL，或者我是否需要找到解决方法？

Answer 1

@PeterCsala 是正确的。问题是 PostgreSQL 准备查询服务器端，因此在 C# 世界中转换参数没有帮助。铸造必须在 SQL 世界中完成。

工作代码变为：

await using var connection = new NpgsqlConnection(_configuration.ConnectionString);

return await connection.QueryAsync<Diamond>(
  @"SELECT
      id,
      name
    FROM
      product
    WHERE
      @Names::text[] IS NULL OR name = ANY(@Names);",
  new
  {
      Names = Names,
  });

当数组参数的值为 null 时无法确定其类型

Cannot determine type of array parameter when its value is null

c#

postgresql

npgsql

dapper