使用 Android 在 SQLite 数据库中查找重复条目

Question

我在 Android 中使用 SQLite 数据库，用户必须输入名称、ip 和 url，然后将其保存在数据库中。我希望能够识别名称列中是否有双重条目，但我不知道如何对其进行编程。我认为创建专栏UNIQUE 是正确的方式...

我的 SQLAdapter：

public class ProjectsDBAdapter {

 public static final String KEY_ROWID = "_id";
 public static final String KEY_PROJECTNAME = "projectname";
 public static final String KEY_ROUTERIP = "routerip";
 public static final String KEY_URL = "url";
 public static final String KEY_CALIMERO = "calimero";

 private static final String TAG = "ProjectsDBAdapter";
 private DatabaseHelper mDbHelper;
 private SQLiteDatabase mDb;

 private static final String DATABASE_NAME = "KNXTable";
 private static final String SQLITE_TABLE = "Project";
 private static final int DATABASE_VERSION = 1;

 private final Context mCtx;

 private static final String DATABASE_CREATE =
  "CREATE TABLE if not exists " + SQLITE_TABLE + " (" +
  KEY_ROWID + " integer PRIMARY KEY autoincrement," +
  KEY_ROUTERIP + "," +
  KEY_PROJECTNAME + "," +
  KEY_URL + "," +
  KEY_CALIMERO + "," +
  "UNIQUE("+KEY_PROJECTNAME+")"+");";

 private static class DatabaseHelper extends SQLiteOpenHelper {

  DatabaseHelper(Context context) {
   super(context, DATABASE_NAME, null, DATABASE_VERSION);
  }

  @Override
  public void onCreate(SQLiteDatabase db) {
   //invoked when the database is created, 
   //this is where we can create tables and columns to them, create views or triggers.
   Log.w(TAG, DATABASE_CREATE);
   db.execSQL(DATABASE_CREATE);
  }

  public long createProject(String ip, String name, 
   String url, String calimero) {

  ContentValues initialValues = new ContentValues();
  initialValues.put(KEY_ROUTERIP, ip);
  initialValues.put(KEY_PROJECTNAME, name);
  initialValues.put(KEY_URL, url);
  initialValues.put(KEY_CALIMERO, calimero);

  return mDb.insert(SQLITE_TABLE, null, initialValues);
  }

希望您能给我一些提示，我已经尝试在创建表时使用 UNIQUE 但没有成功...

更新

SQLiteAdapter 中的方法：

 public long createProject(String ip, String name, 
   String url, String calimero) {

  ContentValues initialValues = new ContentValues();
  initialValues.put(KEY_ROUTERIP, ip);
  initialValues.put(KEY_PROJECTNAME, name);
  initialValues.put(KEY_URL, url);
  initialValues.put(KEY_CALIMERO, calimero);

  return mDb.insertOrThrow(SQLITE_TABLE, null, initialValues);
 }

我活动中的调用：

 //DATABASE
 // Add project to Database
 dbHelper = new ProjectsDBAdapter(this);
 dbHelper.open();

 //Add Strings to database
 dbHelper.insertSomeProjects(IP, Name, URL, Calimero);
 //Generate ListView from SQLite Database
 displayListView();

和 logcat 输出：

01-27 00:02:56.555: E/AndroidRuntime(28526): FATAL EXCEPTION: main
01-27 00:02:56.555: E/AndroidRuntime(28526): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.bertrandt.bertrandtknx/de.bertrandt.bertrandtknx.ProjectList}: android.database.sqlite.SQLiteConstraintException: error code 19: constraint failed
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.app.ActivityThread.access$600(ActivityThread.java:128)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.os.Looper.loop(Looper.java:137)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.app.ActivityThread.main(ActivityThread.java:4514)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at java.lang.reflect.Method.invokeNative(Native Method)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at java.lang.reflect.Method.invoke(Method.java:511)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at dalvik.system.NativeStart.main(Native Method)
01-27 00:02:56.555: E/AndroidRuntime(28526): Caused by: android.database.sqlite.SQLiteConstraintException: error code 19: constraint failed
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.database.sqlite.SQLiteStatement.native_executeInsert(Native Method)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.database.sqlite.SQLiteStatement.executeInsert(SQLiteStatement.java:113)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.database.sqlite.SQLiteDatabase.insertWithOnConflict(SQLiteDatabase.java:1839)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.database.sqlite.SQLiteDatabase.insertOrThrow(SQLiteDatabase.java:1738)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at SQLite.ProjectsDBAdapter.createProject(ProjectsDBAdapter.java:89)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at SQLite.ProjectsDBAdapter.insertSomeProjects(ProjectsDBAdapter.java:140)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at de.bertrandt.bertrandtknx.ProjectList.setup(ProjectList.java:120)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at de.bertrandt.bertrandtknx.ProjectList.onCreate(ProjectList.java:55)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.app.Activity.performCreate(Activity.java:4562)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1053)
01-27 00:02:56.555: E/AndroidRuntime(28526):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
01-27 00:02:56.555: E/AndroidRuntime(28526):    ... 11 more

解决方案

//Add Strings to database
try {
     dbHelper.insertSomeProjects(IP, Name, URL, Calimero);
} catch (SQLiteException exception) {
     Log.d("SQLite", "Error"+exception.toString());
     Toast.makeText(getApplicationContext(),
        "Name is duplicated", Toast.LENGTH_SHORT).show();
            exception.printStackTrace();
}

Answer 1

将 UNIQUE 声明放在列定义部分，如此相关问题所示：

SQLite table constraint - unique on multiple columns

您的示例在 UNIQUE 子句中只有一个列，并且您可能希望在发生冲突时使用不同的策略（例如，可能拒绝插入而不是替换）

CREATE TABLE a (i INT, j INT, UNIQUE(i) ON CONFLICT REPLACE);

Answer 2

您可以将列创建为主键。例如：

"CREATE TABLE mytable ("
"field1 text,"
"field2 text,"
"field3 integer,"
"PRIMARY KEY (field1)"
");"

现在，当您尝试在此列 (field1) 中插入重复值时，您的代码会抛出 SQLException。您需要抓住SQLException 并采取适当的行动。

如果您没有太多要处理的行，您应该考虑填充一个包含所有名称的ArrayList，并使用myArrayList.contains(myNameVariable) 来检查一个名称是否已经被之前处理过。然后，您将能够避免实际执行 SQL 语句来查看它是否抛出异常。