Sqlite：检查数据库是否存在 [英] Sqlite: check if database exist

问题描述

我正在使用phonegap开发一个移动应用程序，将一些数据存储到本地数据库（sqlite DB）。
我需要知道数据库是否存在，并确定哪个进程需要执行。

I am developing a mobile application using phonegap that store some data into the local database (sqlite DB). I need to know if the database exist or not, and that to determine which process need to execute.

var database = window.openDatabase("my_db", "1.0", "sample DB", 30000);
if (check_db_exist()) {
    process_1();
}
else
{
    process_2();
}

推荐答案

，我需要检查应用程序是否已经创建了数据库（旧数据库），如果是这样，则将所有数据导出到新数据库（新的和改进的数据库），然后删除此数据库。

I needed to do something similar, I needed to check if the application had a db already created (legacy DB) and if so export all the data to the new db (new and improved DB) and then delete this DB.

背景信息：我从简单的键值表移动到具有级联等的复杂的关系数据库。

Background Info: I was moving from simple keyvalue tables to complex relational DB with cascades etc.

function onDeviceReady() {
    // CHECK IF LEGACY DATABASE EXISTS. IF DOES EXPORT EXISTING DATA TO NEW DB THEN DELETE LEGACY
    window.resolveLocalFileSystemURL(cordova.file.applicationStorageDirectory + "/databases/<DatabaseName>.db", exportToNewDB, setupDB);
}

注意：如果文件存在（成功），那么我们需要执行导出代码在这里，然后删除文件，所以这个方法将总是失败。如果文件不存在 - 用户已经导出到新的数据库，或者他们是我们的新用户，从来没有遗留数据库。

Note: If file exists (success), then we need to do our export code in here, then delete file so this method will always fail. If file doesn't exist - user has already exported to new DB or they our new user and never had legacy DB.

// Fail Method
function setupDB() {
    newDB = window.sqlitePlugin.openDatabase({ name: "<NewImprovedDBName>.db" });
    newDB.transaction(sql.initDB, sql.errorCallback, sql.successCallBack);
}
// Success Method
function exportToNewDB() {
    db = window.sqlitePlugin.openDatabase({ name: "<LegacyDBName>.db" });
    db.transaction(function (tx) {
         setupDB();
         // Insert Export code Here

         // Delete DB
         window.sqlitePlugin.deleteDatabase("<LegacyDBName>.db", sqlSuccess, sqlFail);
    }, sqlFail);
}

回答您的问题：

window.resolveLocalFileSystemURL(cordova.file.applicationStorageDirectory + "/databases/my_db.db", process_1, process_2);

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