尝试从具有动态条件的 Android 房间持久性库中获取平均值

Question

我正在尝试使用 Android Room Persistence Library 在两个条件下获取平均值，我的实体如下所示：

public class FinishedTask {
    private static final String TASK_NAME_COLUMN = "taskName";
    private static final String DEPARTMENT_NAME_COLUMN = "departmentName";
    private static final String EMPLOYEE_NAME_COLUMN = "employeeName";
    private static final String TIME_UNTIL_DOME_NAME_COLUMN = "timeUntilDoneName";
    private static final String SAVED_DATE_NAME_COLUMN = "savedDateName";

    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "id")
    private long id = 0;

    @ColumnInfo(name = "passedMilliseconds")
    private long passedMilliseconds = 0;

    @ColumnInfo(name = TASK_NAME_COLUMN)
    private String  taskName = TASK_NAME_COLUMN;

    @ColumnInfo(name = DEPARTMENT_NAME_COLUMN)
    private String departmentName = DEPARTMENT_NAME_COLUMN;

    @ColumnInfo(name = EMPLOYEE_NAME_COLUMN)
    private String employeeName = EMPLOYEE_NAME_COLUMN;

    @ColumnInfo(name = TIME_UNTIL_DOME_NAME_COLUMN)
    private long timeUntilDone = 0;


    @ColumnInfo(name = SAVED_DATE_NAME_COLUMN)
    private long savedDate = 0;

    public FinishedTask(){}
}

我的查询如下所示：

@Query("SELECT AVG(timeUntilDoneName) FROM finishedTasks WHERE :column1=:value1 AND :column2=:value2")
Single<Long> getAverageTime(String column1, String value1, String column2, String value2);

我得到错误：

Query returned empty result set: SELECT AVG(timeUntilDoneName) FROM finishedTasks WHERE ?=? AND ?=?

当我将查询更改为：

@Query("SELECT AVG(timeUntilDoneName) FROM finishedTasks WHERE taskName=:value1 AND :departmentName=:value2")
Single<Long> getAverageTime(String value1, String value2);

一切正常，符合预期。我做错了什么？

Answer 1

只能在SQLite本身支持占位符的地方使用占位符，SQLite不支持用占位符替换列名。

尝试从具有动态条件的 Android 房间持久性库中获取平均值

Try to get average value from Android Room Persistence Library with dynamic conditions

android

android-room