检查Android中的应用程序数据库中是否存在列

Question

在 Android 中是否有一种很好的方法来查看应用程序数据库的表中是否存在列？ （我知道已经有类似的问题，但似乎没有任何特定于 Android 的问题。）

Answer 1

cursor.getColumnIndex(String columnName) 如果该列不存在，则返回 -1。所以我基本上会执行一个简单的查询，比如“SELECT * FROM xxx LIMIT 0,1”，并使用光标来确定你正在寻找的列是否存在

或

您可以尝试查询“SELECT theCol FROM xxx”列并捕获异常

Answer 2

我的函数基于@martinpelants 的回答：

private boolean existsColumnInTable(SQLiteDatabase inDatabase, String inTable, String columnToCheck) {
    Cursor mCursor = null;
    try {
        // Query 1 row 
        mCursor = inDatabase.rawQuery("SELECT * FROM " + inTable + " LIMIT 0", null);

        // getColumnIndex() gives us the index (0 to ...) of the column - otherwise we get a -1
        if (mCursor.getColumnIndex(columnToCheck) != -1)
            return true;
        else
            return false;

    } catch (Exception Exp) {
        // Something went wrong. Missing the database? The table?
        Log.d("... - existsColumnInTable", "When checking whether a column exists in the table, an error occurred: " + Exp.getMessage());
        return false;
    } finally {
        if (mCursor != null) mCursor.close();
    }
}

只需调用：

boolean bla = existsColumnInTable(myDB,"MyTable","myColumn2check");

Answer 3

我实际上写了这个看起来很干净的函数：

private boolean field_exists( String p_query )
{
    Cursor mCursor  = mDb.rawQuery( p_query, null );

    if  (  ( mCursor != null ) && ( mCursor.moveToFirst()) )
    {
        mCursor.close();
        return true ;
    }

    mCursor.close();
    return false ;
}

我这样称呼它：

if  ( field_exists( "select * from sqlite_master "              
    + "where name = 'mytable' and sql like '%myfield%' " ))
{
    do_something ;
}

Answer 4

这是我对这个问题的解决方案，它稍微增加了柔印的解决方案。

您可以将此方法放在任何类中，也许是您的 SQLiteOpenHelper 扩展类。

public static boolean columnExistsInTable(SQLiteDatabase db, String table, String columnToCheck) {
    Cursor cursor = null;
    try {
        //query a row. don't acquire db lock
        cursor = db.rawQuery("SELECT * FROM " + table + " LIMIT 0", null);

        // getColumnIndex()  will return the index of the column 
        //in the table if it exists, otherwise it will return -1
        if (cursor.getColumnIndex(columnToCheck) != -1) {
            //great, the column exists
            return true;
        }else {
            //sorry, the column does not exist
            return false;
        }

    } catch (SQLiteException Exp) {
        //Something went wrong with SQLite. 
        //If the table exists and your query was good,
        //the problem is likely that the column doesn't exist in the table.
        return false;
    } finally {
        //close the db  if you no longer need it
        if (db != null) db.close();
        //close the cursor 
        if (cursor != null) cursor.close();
    }
}

Answer 5

如果你使用 ActiveAndroid

public static boolean createIfNeedColumn(Class<? extends Model> type, String column) {
        boolean isFound = false;
        TableInfo tableInfo = new TableInfo(type);

        Collection<Field> columns = tableInfo.getFields();
        for (Field f : columns) {
            if (column.equals(f.getName())) {
                isFound = true;
                break;
            }
        }
        if (!isFound) {
            ActiveAndroid.execSQL("ALTER TABLE " + tableInfo.getTableName() + " ADD COLUMN " + column + " TEXT;");
        }
        return isFound;
    }

Answer 6

这是我的测试代码：

String neadle = "id"; //searched field name
String tableName = "TableName";
boolean found = false;

SQLiteDatabase mDb = ActiveAndroid.getDatabase();
Cursor mCursor  = mDb.rawQuery( "SELECT * FROM sqlite_master WHERE name = '"+tableName+"' and sql like '%"+neadle+"%'" , null);
mCursor.moveToFirst();
String fie = ",";

if (mCursor.getCount() > 0) {
    String[] fields = mCursor.getString(mCursor.getColumnIndex("sql")).split(",");
    for (String field: fields) {
        String[] fieldNameType = field.trim().split(" ");
        if (fieldNameType.length > 0){
            fie += fieldNameType[0]+",";
        }
    }
}else {
    //table not exist!
}
if (mCursor != null) mCursor.close();
// return result: 
found = fie.contains(","+neadle+",");

Answer 7

冒着发布相同解决方案但更短的风险。这是基于@flexo 的精简版

  private boolean doesColumnExistInTable(SupportSQLiteDatabase db, String tableName, String columnToCheck) {
        try (Cursor cursor = db.query("SELECT * FROM " + tableName + " LIMIT 0", null)) {
            return cursor.getColumnIndex(columnToCheck) != -1;
        } catch (Exception Exp) {
            // Something went wrong. we'll assume false it doesn't exist
            return false;
        }
    }

在 Kotlin 中

  private fun doesColumnExistInTable(db: SupportSQLiteDatabase, tableName: String, columnToCheck: String): Boolean {
        try {
            db.query("SELECT * FROM $tableName LIMIT 0", null).use { cursor -> return cursor.getColumnIndex(columnToCheck) != -1 }
        } catch (e: Exception) {
            // Something went wrong. we'll assume false it doesn't exist
            return false
        }
    }