将临时值插入表格中的所有列时,它似乎有效。请参阅以下方法并在下面记录。但是,当我测试列是否存在下面的测试方法时,它会返回false,表示该列存在!!
第一段代码显示调用临时值和测试列是否存在的方法。下面的代码段包括日志,表的创建方式以及调用的方法。谢谢!
ContentValues values = setContVal_All_Columns(myTable);
//create row
long insertId = database.insert(myTable, null, values);
System.out.println("Column date exists = " + String.valueOf(doesColumnExist(myTable,"date")));
setContVal_All_Columns方法:
//sets generic content values to initialize row = excluding ID column
private ContentValues setContVal_All_Columns(String myTable) {
ContentValues contentValues = new ContentValues();
Cursor cursor = database.query(myTable,null,null,null,null,null,null);
String[] columnNames = cursor.getColumnNames();
cursor.moveToFirst();
for(String name : columnNames) {
if(!name.equals(IdColumn)) { //excludes Id column
int index = cursor.getColumnIndex(name);
System.out.println("Column name = " + name + " index = " + String.valueOf(index));
System.out.println("Type = " + String.valueOf(cursor.getType(index))); //appears to crash on the getType
if (cursor.getType(index) == 3) { //String
System.out.println("Column is string");
contentValues.put(name, " ");
} else if (cursor.getType(index) == 1) { //integer
contentValues.put(name, 0);
}
}
}
return contentValues;
}
测试如果列存在的方法:总是在日期列上返回-1 ...
private boolean doesColumnExist(String myTable, String myColumn) {
boolean doesExist = true;
Cursor cursor = database.rawQuery("PRAGMA table_info(" + myTable + ")",null);
cursor.moveToFirst();
int value = cursor.getColumnIndex(myColumn);
if(value == -1)
{
doesExist = false;
}
return doesExist;
}
日志信息:
02-16 19:58:42.296 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Column name = date index = 1
02-16 19:58:42.296 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Type = 0
02-16 19:58:42.296 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Column name = name index = 2
02-16 19:58:42.296 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Type = 3
02-16 19:58:42.296 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Column is string
02-16 19:58:42.296 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Column name = altitude index = 3
02-16 19:58:42.296 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Type = 0
02-16 19:58:42.296 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Column name = is_used index = 4
02-16 19:58:42.296 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Type = 0
02-16 19:58:42.296 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Column name = warning index = 5
02-16 19:58:42.296 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Type = 0
02-16 19:58:42.296 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Column name = action index = 6
02-16 19:58:42.296 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Type = 0
02-16 19:58:42.316 9711-9711/com.mycompany.dudesmyreminders I/System.out﹕ Column date exists = false
表格创建方法:
//Database creation sql statement
private static final String SQL_CREATE_SPECIAL_DAYS =
"CREATE TABLE " + dbFields.TABLE_NAME_SPECIAL_DAYS + " (" +
dbFields.COLUMN_SPECIAL_DAYS_ID + INTEGER_PRIMARY_KEY + COMMA_SEP +
dbFields.COLUMN_SPECIAL_DAYS_DATE + TEXT_TYPE + COMMA_SEP +
dbFields.COLUMN_SPECIAL_DAYS_NAME + TEXT_TYPE + COMMA_SEP +
dbFields.COLUMN_SPECIAL_DAYS_ALTITUDE + INTEGER_TYPE + COMMA_SEP +
dbFields.COLUMN_SPECIAL_DAYS_USED + INTEGER_TYPE + COMMA_SEP +
dbFields.COLUMN_SPECIAL_DAYS_WARNING + INTEGER_TYPE + COMMA_SEP +
dbFields.COLUMN_SPECIAL_DAYS_ACTION + INTEGER_TYPE +
// Any other options for the CREATE command
" )";
@Override
public void onCreate(SQLiteDatabase database) {
database.execSQL(SQL_CREATE_SPECIAL_DAYS);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w(MySQLiteHelper.class.getName(),
"Upgrading database from version " + oldVersion + " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS " + dbFields.TABLE_NAME_SPECIAL_DAYS);
onCreate(db);
}
答案 0 :(得分:3)
使用
cursor.moveToFirst();
int value = cursor.getColumnIndex(myColumn);
您假设PRAGMA
将返回单行中的所有列。现在它是如何运作的。来自PRAGMA
文档
PRAGMA table_info在命名表中为每列返回一行。结果集中的列包括列名,数据类型,列是否为NULL以及列的默认值。
因此,您的doesColumnExist()
方法应该类似于
boolean doesExist = false;
Cursor cursor = database.rawQuery("PRAGMA table_info(" + myTable + ")",null);
while (cursor.moveToNext()) {
if (cursor.getString(cursor.getColumnIndex("name")).equals(myColumn)) {
doesExist = true;
break;
}
}
cursor.close();
return doesExist;
此外,请不要忘记关闭Cursor
。
答案 1 :(得分:2)
来自SQLite文档:
PRAGMA table_info(table-name);
该pragma在命名表中为每列返回一行。
因此PRAGMA查询的结果大致如下:
|-------------------------------------------------------
|cid | name | type | not null | dflt_value | pk | // <-- you're trying to find your column names here, but instead they are in each of the rows
|-------------------------------------------------------
| 1 | date | text | 1 | | 0 |
|-------------------------------------------------------
| 2 | name | text | 0 | | 0 |
|-------------------------------------------------------
| 3 | altitude | integer | 1 | | 0 |
|-------------------------------------------------------
.......
|-------------------------------------------------------