为什么在调用数据库呼叫时未定义我的论点？

Question

我正在尝试通过GraphQL解析器返回Postgres DB查询。出于某种原因，结果在我（故意）查询不存在的ID时未定义的返回。当我安装它记录它时，结果总是按预期返回：

result = {
 rows: [],
 ...
}

但是，当我运行并进行查询时，或者当我使用Node Inspect Instex.js时，请让它运行直到调试器为止，它似乎还没有确定结果。当我运行console.log（result）击中调试器时，我会遇到此错误：

debug> console.log(result)
REPL2:1
console.log(result)
            ^

Uncaught ReferenceError: result is not defined
    at REPL2:1:13
    at Script.runInContext (node:vm:139:12)
    at Object.runInContext (node:vm:289:6)
    at REPLServer.controlEval (node:internal/debugger/inspect_repl:578:25)
    at bound (node:domain:421:15)
    at REPLServer.runBound [as eval] (node:domain:432:12)
    at REPLServer.onLine (node:repl:898:10)
    at REPLServer.emit (node:events:527:28)
    at REPLServer.emit (node:domain:475:12)
    at [_onLine] [as _onLine] (node:internal/readline/interface:424:12)

当我从操场上运行查询时，我会得到此错误：

/Users/user/Projects/geolocatr_api/db/queries/user.queries.js:21
          id: user.id,
                   ^

TypeError: Cannot read properties of undefined (reading 'id')
    at /Users/user/Projects/geolocatr_api/db/queries/user.queries.js:21:20
    at Query.<anonymous> (/Users/user/Projects/geolocatr_api/node_modules/pg-pool/index.js:417:18)
    at Query.handleReadyForQuery (/Users/user/Projects/geolocatr_api/node_modules/pg/lib/query.js:138:12)
    at Client._handleReadyForQuery (/Users/user/Projects/geolocatr_api/node_modules/pg/lib/client.js:290:19)
    at Connection.emit (node:events:527:28)
    at /Users/user/Projects/geolocatr_api/node_modules/pg/lib/connection.js:114:12
    at Parser.parse (/Users/user/Projects/geolocatr_api/node_modules/pg-protocol/dist/parser.js:40:17)
    at Socket.<anonymous> (/Users/user/Projects/geolocatr_api/node_modules/pg-protocol/dist/index.js:11:42)
    at Socket.emit (node:events:527:28)
    at addChunk (node:internal/streams/readable:324:12)

Node.js v18.0.0
error Command failed with exit code 1.

我真的不确定为什么我的控制台日志似乎看到了某些东西，但是节点却没有。否则，当将表格中存在的ID传递时，它可以按预期工作。

代码：

// Resolver

  Query: {
    user: ( _, { id } ) => {
      console.log({id}); // Node recognizes this as the correct number
      return getUserById(id);
    },
  },


// DB Query Function

const getUserById = (id) => {
  return new Promise(function(resolve, reject) {
    db.query(
      `
        SELECT id, first_name, email, phone
        FROM users
        WHERE id = $1;
      `,
      [id],
      function(err, result) {
        // debugger; // Result comes back as not defined
        if (!result.rows) { // Will not run this if block
          console.log(result.rows);
          reject("Could not find user.");
        }
        if (err) reject(err);
        const user = rows[0];

        resolve({
           id: user.id,
           firstName: user.first_name,
           email: user.email,
           phone: user.phone,
        });
      }
    );
  });
};

Answer 1

通常使用这些（err，结果）=＆gt; {...}回调，您检查err first ，因为如果是真实，第二个参数很有可能不会定义。

您还应返回在检测到错误以防止其余回调执行后。

fyi， node-postgresl node-postgresl 在本地支持承诺，因此无需明确创建一个。在下面，我将您的代码转换为异步函数，以利用这一点。

const getUserById = async (id) => {
  const { rows } = await db.query({
    text: "SELECT id, first_name as firstName, email, phone FROM users WHERE id = $1",
    values: [id],
  });

  // `rows` is always an array so check the length
  if (rows.length !== 1) {
    throw new Error(`Could not find user by id [${id}]`);
  }

  return rows[0];
};