在Android中,有没有一种简单的方法可以查看应用程序数据库中的表中是否存在某个列?(我知道已经有类似于这个问题的问题了,但好像没有任何一个是特定于Android的。)
cursor.getColumnIndex(String columnName)
如果该列不存在,则返回-1。因此,我基本上会执行一个简单的查询,例如"SELECT * FROM xxx LIMIT 0,1" ,并使用游标确定您要查找的列是否存在。
或者,您可以尝试查询列"SELECT theCol FROM xxx"并捕获异常。
根据 @martinpelants 的回答,我的函数如下:
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();
}
}
只需拨打电话:
boolean bla = existsColumnInTable(myDB,"MyTable","myColumn2check");
finally
块中关闭游标! - WonderCsaboprivate 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 ;
}
这是我对问题的解决方案,它在flexo的解决方案基础上进行了一些补充。
你可以将此方法放置在任何类中,例如扩展SQLiteOpenHelper的类中。
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();
}
}
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;
}
有可能只是发表了相同但更短的解决方案。这是基于@flexo的版本进行简化的。
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;
}
}
而在 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
}
}
columnToCheck
是什么? - Abdullah JacksicolumnToCheck
是我想要检查其是否存在于表格中的列的字符串名称。 - scottyab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+",");