Question

我正在使用Room persistent library。我要求在一个表中添加两个主键，其中一个主键应该是自动增量。我不知道实现此目的的确切语法。下面是我的Model类：

@Entity(tableName = "newsPapers", primaryKeys = 
{"news_paper_id","news_paper_name"})
public class SelectNewsModel {

private int news_paper_id;

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

@ColumnInfo(name = "news_paper_name")
private String newsPaperName;
}

我想制作＆＃34; news_paper_id＆＃34;自动递增。我该怎么做？

Answer 1

我找到了解决这个问题的另一种方法，因为根据我的知识，在一些R＆amp; D之后，我们不能在复合主键中拥有自动增量属性。所以我在这里使用了索引和唯一约束，因为Room到目前为止还没有直接的UNIQUE约束。以下是我的工作代码：

@Entity(tableName = "newsPapers", indices = {@Index(value = 
       {"news_paper_name"}, unique = true)})
public class SelectNewsModel {

    @PrimaryKey(autoGenerate = true)
    private int news_paper_id;

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

    @ColumnInfo(name = "news_paper_name")
    private String newsPaperName;
}

Answer 2

Priyanka Alachiya 的答案是正确的，但我需要在Kotlin进行采样...

对于Kotlin：

if let array = dictionary["array"] as? [String] {
    print(array, array.isEmpty)
}
if let string = dictionary["string"] as? String {
    print(string, string.isEmpty)
}

Here Kotlin solution

Answer 3

您可以将 Integer 类型用于news_paper_id，然后设置news_paper_id

@Entity(tableName = "newsPapers", primaryKeys = 
{"news_paper_id","news_paper_name"})
public class SelectNewsModel {

 @PrimaryKey(autoGenerate = true)
private Integer news_paper_id;

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

@ColumnInfo(name = "news_paper_name")
private String newsPaperName;
}

如何在Room持久性库中使用复合主键时使主键自动递增？

3 个答案: