Flutter Firestore where子句使用地图 [英] Flutter Firestore where clause using map

问题描述

发布新活动后，我将新的发布文档添加到集合中. 在此文档中，我有一张地图，用户可以在其中向事件添加确认以将其标记为true并添加自己的ID.

var snap = await Firestore.instance
        .collection('user_posts')        
        .where("confirmations.${user.id}",isEqualTo: true)
        .getDocuments();

使用此代码段，我可以获取用户确认的所有帖子.这里的问题是要获得此索引，则需要执行该查询的索引.而且该索引不能是通用的.我无法为每个用户创建索引.

关于如何获得它的一些想法?

谢谢！

解决方案

您需要将confirmations字段转换为数组，并使用(相对较新的)array-contains和arrayUnion操作.

具有类似数组的等效查询将变为:

var snap = await Firestore.instance
    .collection('user_posts')        
    .where("confirmations", arrayContains: user.id)
    .getDocuments();

这样，您只需要在confirmations上的索引，该索引就会自动添加.

有关这些的更多信息，请参见:

• 博客文章，介绍了这些操作
• 有关更新数组的文档
• 有关数组成员资格查询的文档

When a new activity is posted i add a new post document into the collection. Inside this document i have a map where users add confirmation to the event marking it as true and adding his own id.

var snap = await Firestore.instance
        .collection('user_posts')        
        .where("confirmations.${user.id}",isEqualTo: true)
        .getDocuments();

With this snippet i'm able to get all the posts confirmed by the user. The issue here is to get this a index is required to perform this query. And this index can't be generic. I can't create a index for each user.

Some idea of how to get it?

Thanks!!

解决方案

You'll want to turn the confirmations field into an array, and use the (relatively recent) array-contains and arrayUnion operations.

The equivalent query with an array like that would become:

var snap = await Firestore.instance
    .collection('user_posts')        
    .where("confirmations", arrayContains: user.id)
    .getDocuments();

And this way you only need an index on confirmations, which is added automatically.

For more on these see:

• the blog post introducing these operations
• the documentation on updating arrays
• the documentation on array membership queries

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