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android - 尝试从具有动态条件的 Android Room Persistence Library 中获取平均值

问题描述

如果使用 Android Room Persistence Library 的两个条件，我试图获得平均值，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);

我得到了错误：

查询返回空结果集：SELECT AVG(timeUntilDoneName) FROM finishedTasks WHERE ?=? 和？=？

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，如预期的那样。我究竟做错了什么？

标签： androidandroid-room

解决方案

您只能在 SQLite 本身支持占位符的情况下使用占位符，并且 SQLite 不支持用占位符替换列名。

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