问题描述
我有一个关于firebase中的firestore数据库的问题.
I have a question regarding the firestore db from firebase.
我有一个文档X，其中包含一个名为users的字段，该字段是一个引用users集合内用户的对象.
I have a document X that contains a field called users that is an object with references to users inside the users collection.
看起来与此类似:
families: [{
xyz: {
name:'foobar',
users: {
john: 'users/john', //reference to another document
mike: 'users/mike' //reference to another document
}
}
},
...]
如何查询firestore数据库以获取具有用户名称"john"的所有文档(来自familys集合)?
How can I query the firestore db to get all documents (from the families collection) that have a user with the name 'john'?
我没有运气就尝试了以下方法:
I tried the following without luck:
db.collection('families')
.where('users.john', '<', '')
但是它只返回一个空数组.
But it only returns an empty array.
如果我将用户条目从key:reference切换到key:string对象，它将起作用.但是我想使用Refreences，而不是字符串.
If I switch the users entry from key:reference to key:string object it works. But I want to work with refrences and not strings.
推荐答案
Firestore无法提供查询字段是否存在的方法.它用于查找文档的索引基于属性的 values .现在，您的值是文档参考，因此您只能查询它们的参考值.
Firestore doesn't provide a way to query for the simple existence of fields. The indexes it uses to find documents are based on the values of a property. Right now, your values are document references, so you can only query against their reference values.
如果您想知道文档中是否存在某些内容，则可以为其创建一个带有布尔值的新字段.然后，您可以查询是非.
If you want to know if a something exists in a document, you could create a new field for it with a boolean value. You can then query that for true or false.
families: [{
xyz: {
name:'foobar',
users: {
john: 'users/john', //reference to another document
mike: 'users/mike' //reference to another document
},
users_exists: {
john: true,
mike: true
}
}
},
有了上面的users_exists，现在您可以像这样查询:
With users_exists in place above, now you can query like this:
db.collection('families')
.where('users_exists.john', '==', true)
NoSQL数据建模的一般规则是以适合您要执行的查询的任何方式进行.有时，这涉及复制数据以适合那些查询.
The general rule for NoSQL data modeling is to do it in whatever way suits the queries you intend to perform. Sometimes this involves duplicating data to suit those queries.
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