根据来自 firestore 的文档查询 collection 创建列表

Question

我能够在 flutter 应用程序中成功地从 firestore collection 中获取文档并创建列表视图构建器。除此之外，我想创建一个特定字段的列表，该列表对 collection.

中的所有文档都是通用的

例如，每个文档都有 username 的公共字段，在从 firestore collection 获取所有文档后，我想创建一个用户名列表 List usernames = [];，我可以在其中添加 collection.

中的所有用户名

Query query2 =   FirebaseFirestore.instance
        .collection('users');


StreamBuilder<QuerySnapshot>(
                 stream: query2.snapshots(),

              builder: (BuildContext context,AsyncSnapshot<QuerySnapshot> snapshot) {

                if (snapshot.hasError) {
                  return Text('Something went wrong');
                }

                if (snapshot.connectionState == ConnectionState.waiting) {
                  return Text("Loading");
                }

                return ListView.builder(
                  itemCount: snapshot.data.docs.length,
                  itemBuilder: (context, index){

                    return ListTile(title:Text(snapshot.data.docs[index]['username'] ?? "",
                                    subtitle:Text(snapshot.data.docs[index]['email'] ?? ""
                  ),);
                  });
                }
              )

上面的代码工作正常我想创建一个单独的列表用于用户名 List usernames = [];

我该怎么做？请指教

Answer 1

var usernames = snapshot.data.docs.map((e) => e['username']);

Answer 2

试试这个：

查询query2 = FirebaseFirestore.instance .collection('users').where("用户名",isNull: false );

StreamBuilder( 流：query2.snapshots(),

          builder: (BuildContext context,AsyncSnapshot<QuerySnapshot> snapshot) {

            if (snapshot.hasError) {
              return Text('Something went wrong');
            }

            if (snapshot.connectionState == ConnectionState.waiting) {
              return Text("Loading");
            }

            return ListView.builder(
              itemCount: snapshot.data.docs.length,
              itemBuilder: (context, index){

                return ListTile(title:Text(snapshot.data.docs[index]['username'] ?? "",
                                subtitle:Text(snapshot.data.docs[index]['email'] ?? ""
              ),);
              });
            }
          )

这基本上是检查整个集合和 returns username 不为空的数据。

根据来自 firestore 的文档查询 collection 创建列表

create the list from the query collection of documents from firestore

list

firebase

flutter

google-cloud-firestore

flutter-listview