是否可以在android数据库中的文本字段上应用主键 [英] Is it possible to apply primary key on the text fields in android database

问题描述

我创建了一个简单的表格，其中包含人员的姓名和电子邮件 ID.当我给出这样的创建查询时:

I have created a simple table that contains the name and email id's of the persons. When i am giving the create query like this:

创建表格联系人(姓名文本不为空，电子邮件文本主键不为空)；"

但这行不通.运行时我没有收到任何异常或错误，主键也没有工作.在使用 SQLite 浏览器浏览表格时，我观察到只有四种数据类型:

But this is not working. I'm not getting any exception or error while running nor the primary key is working. While browsing the table using SQLite browser i observed that there are only four data types:

是否可以只在整数上应用主键?如果我想在文本字段上使用主键，会发生什么情况.谢谢你.这是我使用的代码:

Is it possible to apply primary key only on integer? What is the case if i want primary key on text fields. Thank you. This is the code that i used:

public class DBAdapter {

public static final String KEY_ROWID = "_id";
public static final String KEY_NAME = "name";
public static final String KEY_EMAIL = "email";
private static final String TAG = "DBAdapter";

private static final String DATABASE_NAME = "MyDB";
private static final String DATABASE_TABLE = "contacts";
private static final int DATABASE_VERSION = 2;

private static final String DATABASE_CREATE =
    "create table contacts (_id integer primary key autoincrement, "
    + "name text not null, email text not null);";

private final Context context;    

private DatabaseHelper DBHelper;
private SQLiteDatabase db;

public DBAdapter(Context ctx) 
{
    this.context = ctx;
    DBHelper = new DatabaseHelper(context);
}

private static class DatabaseHelper extends SQLiteOpenHelper 
{
    DatabaseHelper(Context context) 
    {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) 
    {
        try {
            db.execSQL(DATABASE_CREATE);    
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
    {
        Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
                + newVersion + ", which will destroy all old data");
        db.execSQL("DROP TABLE IF EXISTS contacts");
        onCreate(db);
    }
}    

//---opens the database---
public DBAdapter open() throws SQLException 
{
    db = DBHelper.getWritableDatabase();
    return this;
}

//---closes the database---    
public void close() 
{
    DBHelper.close();
}

//---insert a contact into the database---
public long insertContact(String name, String email) 
{
    ContentValues initialValues = new ContentValues();
    initialValues.put(KEY_NAME, name);
    initialValues.put(KEY_EMAIL, email);
    return db.insert(DATABASE_TABLE, null, initialValues);
}

//---deletes a particular contact---
public boolean deleteContact(long rowId) 
{
    return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
}

//---retrieves all the contacts---
public Cursor getAllContacts() 
{
    return db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME,
            KEY_EMAIL}, null, null, null, null, null);
}

//---retrieves a particular contact---
public Cursor getContact(long rowId) throws SQLException 
{
    Cursor mCursor =
            db.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,
            KEY_NAME, KEY_EMAIL}, KEY_ROWID + "=" + rowId, null,
            null, null, null, null);
    if (mCursor != null) {
        mCursor.moveToFirst();
    }
    return mCursor;
}

//---updates a contact---
public boolean updateContact(long rowId, String name, String email) 
{
    ContentValues args = new ContentValues();
    args.put(KEY_NAME, name);
    args.put(KEY_EMAIL, email);
    return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
}
}

推荐答案

按照 sqlite 文档的 faq，使用 TEXT 作为主键的数据类型应该可以工作.

as per the faq of sqlite documentation, using TEXT as a datatype for primary key should work.

我使用了您的查询，现在已创建表.

i used your query and here it is, the table is created.

CREATE TABLE contacts ( email text primary key not null, name text not null);

INSERT INTO contacts VALUES ('[e-mail]', 'sample')
INSERT INTO contacts VALUES ('[e-mail]', 'sample')

现在是哪里出错了.

当我再次运行时

INSERT INTO contacts VALUES ('[e-mail]', 'sample')

什么都没发生，没有错误.但它没有更新记录.所以我得出的结论是数据完整性存在，但您没有收到有关失败的任何反馈.

nothing happened, no errors. But it did not update the record. so i conclude data integrity is there but you don't get any feedback about the failure.

这篇关于是否可以在android数据库中的文本字段上应用主键的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！