Sqlite：检查数据库是否存在

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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