如何在 Flutter 中使用带有 arrayContains 列表的 where 查询

Question

Map carsMap = {
    "vehicles": [
      {
        "name": "Vehicle1",
        "models": ["bus", "plane", "bicycle"]
      },
      {
        "name": "Vehicle2",
        "models": ["motorcycle", "sporcar", "plane"]
      },
      {
        "name": "Vehicle3",
        "models": ["motorcycle", "plane", "bicycle"]
      }
    ]
  };

我有如上所示的车辆列表，我想查询并显示哪个列表包括飞机和摩托车。我可以使用此代码单查询哪个列表包括飞机，但我不能同时查询哪个列表包括飞机和摩托车。

List<Map> updatedList = carsList
        .where((m) => m.toString().toLowerCase().contains("plane".toLowerCase()))
        .toList();

顺便说一下，飞机和摩托车只是一个例子，这些数据可以根据用户输入而改变。所以我想根据用户输入动态查询。

我怎样才能通过 where 查询或其他方式来做到这一点。

这是我使用 Firebase 的源代码。

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';

class Home1 extends StatefulWidget {
  @override
  _Home1State createState() => _Home1State();
}

class _Home1State extends State<Home1> {
  final _firestore = FirebaseFirestore.instance;

  @override
  Widget build(BuildContext context) {
    CollectionReference tarifRef = _firestore.collection("vehicles");

    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            StreamBuilder<QuerySnapshot>(
              stream: tarifRef.snapshots(),
              builder: (BuildContext context, AsyncSnapshot asyncsnapshot) {
                if (asyncsnapshot.hasError) {
                  return Center(
                    child: Text("Error"),
                  );
                } else {
                  if (asyncsnapshot.hasData) {
                    List<DocumentSnapshot> listOfDocumentSnapshot =
                        asyncsnapshot.data.docs;
                    return Flexible(
                      child: ListView.builder(
                        itemCount: listOfDocumentSnapshot.length,
                        itemBuilder: (context, index) {
                          return Card(
                            color: Colors.indigo,
                            child: ListTile(
                              title: Text(
                                "${listOfDocumentSnapshot[index]["name"]}",
                                style: TextStyle(
                                  fontSize: 20,
                                  color: Colors.white,
                                ),
                              ),
                              subtitle: Text(
                                "${listOfDocumentSnapshot[index]["vehicleList"]}",
                                style: TextStyle(
                                  fontSize: 15,
                                  color: Colors.white,
                                ),
                              ),
                              trailing: IconButton(
                                icon: Icon(
                                  Icons.delete,
                                  color: Colors.white,
                                ),
                                onPressed: () async {
                                  await listOfDocumentSnapshot[index]
                                      .reference
                                      .delete();
                                },
                              ),
                            ),
                          );
                        },
                      ),
                    );
                  } else {
                    return Center(
                      child: CircularProgressIndicator(),
                    );
                  }
                }
              },
            ),
          ],
        ),
      ),
    );
  }
}

Answer 1

您的条件需要一个逻辑或：

  List<Map> updatedList = carsMap['vehicles']
      .where((m) =>  m.toString().toLowerCase().contains("plane".toLowerCase())) || 
m.toString().toLowerCase().contains("motorcyle".toLowerCase()))
      .toList();

你也可以用这个

  var carsMap = {
    'vehicles': [
      {
        'name': 'Vehicle1',
        'models': ['bus', 'plane', 'bicycle']
      },
      {
        'name': 'Vehicle2',
        'models': ['motorcycle', 'sporcar', 'plane']
      },
      {
        'name': 'Vehicle3',
        'models': ['motorcycle', 'plane', 'bicycle']
      }
    ]
  };
  var n = carsMap['vehicles'].where((element) =>
      (element['models'] as List).contains('plane') ||
      (element['models'] as List).contains('motorcycle'));

如果要动态查询

在过滤器列表中添加过滤器键并创建一个函数来检查元素是否与过滤器具有共同值

  List filters = [
    'motorcycle',
    'plane'
  ];
  filter(e){
    for(var f in filters)
      if(e['models'].contains(f)) return true;
    return false;
  }
  var n = carsMap['vehicles'].where(filter);