如何在Room数据库中从Query中获取包含别名的数据

因为我们在Entity中获取数据只返回对象形式的数据，所以我们如何才能从Query中获取数据

SELECT *,(select count(uid) from UserTest) AS rec_count FROM UserTest

即此字段数据 rec_count

得到解决方案

第1步

首先创建新的Pojo类，在其中编写实体中编写的所有getter和setter，并为计数值包含int getter和setter

实体类：UserTest.java

@Entity
public class UserTest {

    @PrimaryKey(autoGenerate = true)
    private int uid;

    @ColumnInfo(name = "username")
    private String uname;

    @ColumnInfo(name = "image_url")
    private String imageUrl;

    @ColumnInfo(name = "date")
    @TypeConverters({DateConverter.class})
    private Date DATE;

    public UserTest() {
    }

    @Ignore
    public UserTest(int uid) {
        this.uid = uid;
    }

    @Ignore
    public UserTest(String uname, String imageUrl, Date DATE) {
        this.uname = uname;
        this.imageUrl = imageUrl;
        this.DATE = DATE;
    }

    public int getUid() {
        return uid;
    }

    public void setUid(int uid) {
        this.uid = uid;
    }

    public String getUname() {
        return uname;
    }

    public void setUname(String uname) {
        this.uname = uname;
    }

    public String getImageUrl() {
        return imageUrl;
    }

    public void setImageUrl(String imageUrl) {
        this.imageUrl = imageUrl;
    }

    public Date getDATE() {
        return DATE;
    }

    public void setDATE(Date DATE) {
        this.DATE = DATE;
    }
}

新的Pojo类：Result.java

public class Result {

    private int rec_count;

    private int uid;

    private String username;

    private String image_url;

    @TypeConverters({DateConverter.class})
    private Date date;

    public Result() {
    }

    public Result(int uid) {
        this.uid = uid;
    }


    public Result(String uname, String imageUrl, Date DATE) {
        this.username = uname;
        this.image_url = imageUrl;
        this.date = DATE;
    }

    public int getUid() {
        return uid;
    }

    public void setUid(int uid) {
        this.uid = uid;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getImage_url() {
        return image_url;
    }

    public void setImage_url(String image_url) {
        this.image_url = image_url;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public int getRec_count() {
        return rec_count;
    }

    public void setRec_count(int rec_count) {
        this.rec_count = rec_count;
    }
}

第2步：然后在我的Dao类中，即UserDaoTest.java

Witten查询并将返回类型设置为

List<Result>

即

@Query("SELECT *,(select count(uid) from UserTest) AS rec_count FROM UserTest")
    List<Result> getAllUsersData();

这对我有用！

解释

每当我们在dao @Query anotation中编写查询时

在查询中，如果有*它在返回的pojo中找到所有列名，那么我们应该将它们全部包含在返回的pojo中

并且为了在别名中获取数据，我们还应该在返回Pojo类中包含在别名上命名的getter和setter变量

Hope this info will be helpful for others too!

android android-room