问题
How do you insert data into a database in Flutter using the SQFlite plugin?
There are a number of problem solving questions out there but none that I could find to add a canonical answer to. My answer is below.
回答1:
Add the dependencies
Open pubspec.yaml and in the dependency section add the following lines:
sqflite: ^1.0.0
path_provider: ^0.4.1
The sqflite is the SQFlite plugin of course and the path_provider will help us get the user directory on Android and iPhone.
Make a database helper class
I'm keeping a global reference to the database in a singleton class. This will prevent concurrency issues and data leaks (that's what I hear, but tell me if I'm wrong). You can also add helper methods (like insert) in here for accessing the database.
Create a new file called database_helper.dart and paste in the following code:
import 'dart:io' show Directory;
import 'package:path/path.dart' show join;
import 'package:sqflite/sqflite.dart';
import 'package:path_provider/path_provider.dart' show getApplicationDocumentsDirectory;
class DatabaseHelper {
static final _databaseName = "MyDatabase.db";
static final _databaseVersion = 1;
static final table = 'my_table';
static final columnId = '_id';
static final columnName = 'name';
static final columnAge = 'age';
// make this a singleton class
DatabaseHelper._privateConstructor();
static final DatabaseHelper instance = DatabaseHelper._privateConstructor();
// only have a single app-wide reference to the database
static Database _database;
Future<Database> get database async {
if (_database != null) return _database;
// lazily instantiate the db the first time it is accessed
_database = await _initDatabase();
return _database;
}
// this opens the database (and creates it if it doesn't exist)
_initDatabase() async {
Directory documentsDirectory = await getApplicationDocumentsDirectory();
String path = join(documentsDirectory.path, _databaseName);
return await openDatabase(path,
version: _databaseVersion,
onCreate: _onCreate);
}
// SQL code to create the database table
Future _onCreate(Database db, int version) async {
await db.execute('''
CREATE TABLE $table (
$columnId INTEGER PRIMARY KEY,
$columnName TEXT NOT NULL,
$columnAge INTEGER NOT NULL
)
''');
}
}
Insert data
We'll use an async method to do our insert:
_insert() async {
// get a reference to the database
// because this is an expensive operation we use async and await
Database db = await DatabaseHelper.instance.database;
// row to insert
Map<String, dynamic> row = {
DatabaseHelper.columnName : 'Bob',
DatabaseHelper.columnAge : 23
};
// do the insert and get the id of the inserted row
int id = await db.insert(DatabaseHelper.table, row);
// show the results: print all rows in the db
print(await db.query(DatabaseHelper.table));
}
Notes
- You will have to import the
DatabaseHelperclass andsqfliteif you are in another file (like main.dart). - The SQFlite plugin uses a
Map<String, dynamic>to map the column names to the data in each row. - We didn't specify the
id. SQLite auto increments it for us.
Raw insert
SQFlite also supports doing a raw insert. This means that you can use a SQL string. Lets insert the same row again using rawInsert().
db.rawInsert('INSERT INTO my_table(name, age) VALUES("Bob", 23)');
Of course, we wouldn't want to hard code those values into the SQL string, but we also wouldn't want to use interpelation like this:
String name = 'Bob';
int age = 23;
db.rawInsert('INSERT INTO my_table(name, age) VALUES($name, $age)'); // Dangerous!
That would open us up to SQL injection attacks. Instead we can use data binding like this:
db.rawInsert('INSERT INTO my_table(name, age) VALUES(?, ?)', [name, age]);
The [name, age] are filled in for the question mark placeholders in (?, ?). The table and column names are safer to use interpelation for, so we could do this finally:
String name = 'Bob';
int age = 23;
db.rawInsert(
'INSERT INTO ${DatabaseHelper.table}'
'(${DatabaseHelper.columnName}, ${DatabaseHelper.columnAge}) '
'VALUES(?, ?)', [name, age]);
Supplemental code
For your copy-and-paste convenience, here is the layout code for main.dart:
import 'package:flutter/material.dart';
import 'package:flutter_db_operations/database_helper.dart';
import 'package:sqflite/sqflite.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'SQFlite Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(),
);
}
}
class MyHomePage extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('sqflite'),
),
body: RaisedButton(
child: Text('insert', style: TextStyle(fontSize: 20),),
onPressed: () {_insert();},
),
);
}
_insert() async {
// get a reference to the database
// because this is an expensive operation we use async and await
Database db = await DatabaseHelper.instance.database;
// row to insert
Map<String, dynamic> row = {
DatabaseHelper.columnName : 'Bob',
DatabaseHelper.columnAge : 23
};
// do the insert and get the id of the inserted row
int id = await db.insert(DatabaseHelper.table, row);
// raw insert
//
// String name = 'Bob';
// int age = 23;
// int id = await db.rawInsert(
// 'INSERT INTO ${DatabaseHelper.table}'
// '(${DatabaseHelper.columnName}, ${DatabaseHelper.columnAge}) '
// 'VALUES(?, ?)', [name, age]);
print(await db.query(DatabaseHelper.table));
}
}
Going on
- This post is a development from my previous post: Simple SQFlite database example in Flutter. See that post for other SQL operations and advice.
回答2:
get in pubspec.yaml
add
dependency:
sqflite: any,
path_provider: any,
intl: ^0.15.7
- then click package get and package upgrade
来源：https://stackoverflow.com/questions/54097326/how-to-do-a-database-insert-with-sqflite-in-flutter