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Flutter在使用中为数据库创建表之前如何检查数据库是否存在sqflite？

例如，如果我要创建数据库doggie_database.db，如何在创建表时过早地检查它的存在？

final Future<Database> database = openDatabase(
  // Set the path to the database. 
  join(await getDatabasesPath(), 'doggie_database.db'),
  // When the database is first created, create a table to store dogs.
  onCreate: (db, version) {
    // Run the CREATE TABLE statement on the database.
    return db.execute(
      "CREATE TABLE dogs(id INTEGER PRIMARY KEY, name TEXT, age INTEGER)",
    );
  },
  // Set the version. This executes the onCreate function and provides a
  // path to perform database upgrades and downgrades.
  version: 1,
);
4

1 回答 1

11

您可以使用 . 检查数据库是否存在databaseExists(String path)。

https://github.com/tekartik/sqflite/blob/master/sqflite/lib/sqflite.dart（第174行）

/// Check if a database exists at a given path.
///
Future<bool> databaseExists(String path) =>
    databaseFactory.databaseExists(path);

但我认为您担心CREATE TABLE再次调用该声明。如果您指定version. 在内部保留版本，onCreate如果已经指定，则不会调用它。

从同一个文件：

/// If [version] is specified, [onCreate], [onUpgrade], and [onDowngrade] can
/// be called. These functions are mutually exclusive — only one of them can be
/// called depending on the context, although they can all be specified to
/// cover multiple scenarios
///
/// [onCreate] is called if the database did not exist prior to calling
/// [openDatabase]. You can use the opportunity to create the required tables
/// in the database according to your schema
于 2019-07-28T10:27:09.350 回答