Question

我在从表中删除行时遇到问题。

我有2个表，其定义如下：

private static final String DATABASE_TABLEELEMENTS = "elements";
    public static final String KEY_ROWELEMENTID = "_id";
    public static final String KEY_STUDYID = "idstudy";
    public static final String KEY_ELEMENTCODE = "code_element";
    public static final String KEY_ELEMENTNAME = "description_element";


private static final String DATABASE_TABLETIME = "times";
    public static final String KEY_ROWTIME = "_id";
    public static final String KEY_ELEMENTID = "idelement";
    public static final String KEY_HOURDATE = "hour_date";
    public static final String KEY_OBSERVEDYTIME = "observedtime";
    public static final String KEY_OBSERVEDACTIVITY = "observedactivity";

这两个表都是相关的：

elements._id = times.idelement

我想删除表“times”中的所有行，这些行具有用户选择的表“elements”中的“idstudy”：

为此我创建了以下功能：

public void ResetDataStudies(String selectedid) {
  String querytimes = "DELETE FROM "
  + "times"
  + " WHERE "
  + "times.idelement"
  + " IN "
  + "(SELECT "
  + "elements._id"
  + " FROM "
  + "elements"
  + " WHERE "
  + "elements.idstudy = ?)";
  ourDatabase.rawQuery(querytimes, new String[] { selectedid });
}

我没有收到特定错误，但在执行之后数据尚未删除。

见下面的数据类型：

db.execSQL(" CREATE TABLE " + DATABASE_TABLEELEMENTS + " (" +
                     KEY_ROWELEMENTID + " INTEGER UNIQUE PRIMARY KEY AUTOINCREMENT, " +
                     KEY_ELEMENTCODE + " INTEGER NOT NULL, " +
                     KEY_ELEMENTNAME + " TEXT, " +
                     KEY_STUDYID + " TEXT NOT NULL REFERENCES " +  DATABASE_TABLEACOUNT + "("+ KEY_ROWSTUDYID +") ON DELETE CASCADE ");      

             db.execSQL(" CREATE TABLE " + DATABASE_TABLETIME + " (" +
                     KEY_ROWTIME + " INTEGER UNIQUE PRIMARY KEY AUTOINCREMENT, " +
                     KEY_HOURDATE + " INTEGER NOT NULL, " +
                     KEY_OBSERVEDYTIME + " TEXT NOT NULL, " +
                     KEY_OBSERVEDACTIVITY + " TEXT NOT NULL, " +
                     KEY_ELEMENTID + " TEXT NOT NULL REFERENCES " +  DATABASE_TABLEELEMENTS + "("+ KEY_ROWELEMENTID +") ON DELETE CASCADE ");
        }

我已更新了我的语句，但现在我在创建表时收到错误：

cascade语句附近的

错误

Answer 1

创建表时，外键需要为ON DELETE CASCADE。例如

 FOREIGN KEY ("+KEY_ELEMENTID+") REFERENCES "+DATABASE_TABLEELEMENTS+" ("+KEY_ROWELEMENTID+") ON DELETE CASCADE); "

您还必须告诉SQLite强制执行外键（否则会被忽略）。

PRAGMA foreign_keys = ON;

请参阅https://www.sqlite.org/foreignkeys.html。

无法从链接表

1 个答案: