firebase where() 不返回该文档数据？

【问题标题】：firebase where() not returning that docs data?firebase where() 不返回该文档数据？
【发布时间】：2021-02-21 00:51:27
【问题描述】：

这就是我正在尝试做的事情，我正在尝试获取用户的用户名。我有用户的电子邮件，所以我试图搜索文档以找到该电子邮件所在的文档，然后从中获取用户名。

代码：

useEffect(() => {
        auth().onAuthStateChanged((user) => {
            if (user) {
                // User logged in already or has just logged in.
                updateUser(user.email)
            } else {
                // User not logged in or has just logged out.
            }
        });

        //get the username here
        firestore().collection('users').where("email", "==", userCurrent).get().then((doc) => {
            console.log(doc)
        }).catch((error) => { console.log(error) })
    })

当我尝试执行 doc.data() 时，我得到 doc.data 不是函数。当我尝试删除它并调用 doc 查看打印出的内容时，我得到了这个海量数据转储：

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      },
    ],
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             ...(truncated to the first 10000 characters)
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  },
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     ...(truncated to the first 10000 characters)

只想访问作为电子邮件字段 == 当前用户电子邮件的文档的数据

编辑：

firestore().collection('users').where("email", "==", userCurrent).get()
            .then((querySnapshot) => {
                querySnapshot.forEach(doc => {
                    console.log(doc.data())
                })
            })
            .catch((error) => { console.log(error) })

【问题讨论】：

    标签： javascript firebase react-native google-cloud-firestore


    【解决方案1】：

    当您在 Query 对象上调用 get() 时：

    firestore().collection('users').where("email", "==", userCurrent).get()

    它将产生一个QuerySnapshot 对象（不是 DocumentSnapshot）。该 QuerySnapshot 可以包含 0 个或多个文档。即使您认为它将包含一个文档，您至少应该检查它是否包含多个文档：

    firestore().collection('users').where("email", "==", userCurrent).get()
.then((querySnapshot) => {
    if (querySnapshot.docs.length > 0) {
        const documentSnapshot = querySnapshot.docs[0];
        console.log(documentSnapshot.data());
    }
    else {
        // decide what you want to do if the query resulted in no documents.
    }
})
.catch((error) => { console.log(error) })

    您还应该知道 onAuthStateChanged 是异步的，并且在知道任何 user 对象之前立即返回。如果您希望仅在登录完成后执行查询，则您的查询可能位于错误的位置。

    【讨论】：

    • 当我实现这个方法时，console.log(documentSnapshot.data()) 似乎没有被调用（也没有错误）。我在查询之前添加了一个打印语句，并且调用得很好。好像查询没有运行或其他什么。我用我尝试过的另一种方法更新了我的帖子（结果相同）。感谢您的回复！
    • 您没有检查结果集中是否有任何文档。我的代码通过检查 docs 数组的长度来显示这一点。如果没有匹配的文档，您的代码将不会打印任何内容。
    • 哎呀，这很明显。谢谢:)
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