一个人怎么检查，如果一个表存在于Android的SQLite数据库？ [英] How does one check if a table exists in an Android SQLite database?

问题描述

我有一个Android应用程序，需要检查是否有已在数据库中的记录，如果没有，过程中的一些东西，并最终将其插入，并简单地从数据库中读取数据，如果数据确实存在。我使用SQLiteOpenHelper的子类来创建并获得SQLiteDatabase，我想自动把创建表，如果它不存在（因为code这样做是在OnCreate照顾的可擦写实例（ ...） 方法）。

I have an android app that needs to check if there's already a record in the database, and if not, process some things and eventually insert it, and simply read the data from the database if the data does exist. I'm using a subclass of SQLiteOpenHelper to create and get a rewritable instance of SQLiteDatabase, which I thought automatically took care of creating the table if it didn't already exist (since the code to do that is in the onCreate(...) method).

然而，当表还不存在，而第一种方法运行于SQLiteDatabase对象我有一个电话查询（...），我的logcat显示I /数据库的错误（26434）：源码返回：错误code = 1，味精=没有这样的表：应用程序数据，果然，该应用程序数据表不被创建

However, when the table does NOT yet exist, and the first method ran upon the SQLiteDatabase object I have is a call to query(...), my logcat shows an error of "I/Database(26434): sqlite returned: error code = 1, msg = no such table: appdata", and sure enough, the appdata table isn't being created.

为什么任何想法？

我在找任何一个方法来测试，如果表存在（因为如果不是这样，数据的肯定不是它，我不需要看它，直到我写，这似乎创建表正确），还是有办法，以确保它被创建的，仅仅是空的，在时间上为第一次调用查询（...）

I'm looking for either a method to test if the table exists (because if it doesn't, the data's certainly not in it, and I don't need to read it until I write to it, which seems to create the table properly), or a way to make sure that it gets created, and is just empty, in time for that first call to query(...)

修改
这是贴在下面两个答案后：
我想我可能已经找到了问题。我出于某种原因决定，不同的SQLiteOpenHelper本来是要为每个表创建的，即使这两个访问同一个数据库文件。我认为重构是code到只使用一个OpenHelper，并创建两个表里面的OnCreate可以更好地工作...

EDIT
This was posted after the two answers below:
I think I may have found the problem. I for some reason decided that a different SQLiteOpenHelper was supposed to be created for each table, even though both access the same database file. I think refactoring that code to only use one OpenHelper, and creating both tables inside it's onCreate may work better...

推荐答案

是的，原来的理论在我的编辑是正确的：这是造成onCreate方法不能运行的问题，是一个事实，即 SQLiteOpenHelper 的对象应该是指数据库，并没有一个单独的每个表一个。包装这两个表为一个 SQLiteOpenHelper 解决了这个问题。

Yep, turns out the theory in my edit was right: the problem that was causing the onCreate method not to run, was the fact that SQLiteOpenHelper objects should refer to databases, and not have a separate one for each table. Packing both tables into one SQLiteOpenHelper solved the problem.

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