Flutter Firestore where clause using map

问题

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!!

回答1:

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

来源：https://stackoverflow.com/questions/54012380/flutter-firestore-where-clause-using-map