java - SQLite 重复条目

Question

我有以下代码，但我在重复项方面遇到了一些麻烦。我如何修改代码以使其不允许数据库中出现重复项？我用它来驱动 AutoCompleteTextView，所以重复项没有帮助。非常感谢!

package com.giantflyingsaucer;

import android.database.*;
import android.database.sqlite.*;
import android.content.ContentValues;
import android.content.Context;
import android.util.Log;

public class SQLiteCountryAssistant extends SQLiteOpenHelper
{
private static final String DB_NAME = "usingsqlite.db";
private static final int DB_VERSION_NUMBER = 1;
private static final String DB_TABLE_NAME = "countries";
private static final String DB_COLUMN_1_NAME = "country_name";

private static final String DB_CREATE_SCRIPT = "create table " + DB_TABLE_NAME +
                        " (_id integer primary key autoincrement, country_name text not null);)";

private SQLiteDatabase sqliteDBInstance = null;

public SQLiteCountryAssistant(Context context)
{
    super(context, DB_NAME, null, DB_VERSION_NUMBER);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{
    // TODO: Implement onUpgrade
}

@Override
public void onCreate(SQLiteDatabase sqliteDBInstance)
{
    Log.i("onCreate", "Creating the database...");
    sqliteDBInstance.execSQL(DB_CREATE_SCRIPT);
}

public void openDB() throws SQLException
{
    Log.i("openDB", "Checking sqliteDBInstance...");
    if(this.sqliteDBInstance == null)
    {
        Log.i("openDB", "Creating sqliteDBInstance...");
        this.sqliteDBInstance = this.getWritableDatabase();

    }
}

public void closeDB()
{
    if(this.sqliteDBInstance != null)
    {
        if(this.sqliteDBInstance.isOpen())
            this.sqliteDBInstance.close();
    }
}

public long insertCountry(String countryName)
{
    ContentValues contentValues = new ContentValues();
    contentValues.put(DB_COLUMN_1_NAME, countryName);
    Log.i(this.toString() + " - insertCountry", "Inserting: " + countryName);
    return this.sqliteDBInstance.insert(DB_TABLE_NAME, null, contentValues);
}

public boolean removeCountry(String countryName)
{
    int result = this.sqliteDBInstance.delete(DB_TABLE_NAME, "country_name='" + countryName + "'", null);

    if(result > 0)
        return true;
    else
        return false;
}

public long updateCountry(String oldCountryName, String newCountryName)
{
    ContentValues contentValues = new ContentValues();
    contentValues.put(DB_COLUMN_1_NAME, newCountryName);
    return this.sqliteDBInstance.update(DB_TABLE_NAME, contentValues, "country_name='" + oldCountryName + "'", null);
}

public String[] getAllCountries()
{
    Cursor cursor = this.sqliteDBInstance.query(DB_TABLE_NAME, new String[] {DB_COLUMN_1_NAME}, null, null, null, null, null);

    if(cursor.getCount() >0)
    {
        String[] str = new String[cursor.getCount()];
        int i = 0;

        while (cursor.moveToNext())
        {
             str[i] = cursor.getString(cursor.getColumnIndex(DB_COLUMN_1_NAME));
             i++;
         }
        return str;
    }
    else
    {
        return new String[] {};
    }
}
}

Answer 1

一种选择是在实际执行插入之前从 insertCountry 方法调用 removeCountry。或者，您可以将数据库结构修改为country_name text not null unique。如果您未满足约束条件，SQLite 将抛出异常，您需要捕获并适当处理该异常。

最后，另一种选择是尝试在数据库中查询相关字符串，如果存在，则不插入，如果不存在，则插入。