Question

我正在学习如何在Android中使用Room。我有两个表：KeyWordsTable（标识，关键字）和CategoriesTable（标识，imagePath）。我想做这样的事情：用户给一个关键字->检查它属于哪个类别->从CategoriesTable获取imagePath。

我有@Dao界面，并且做过类似的事情

@Query("SElECT image_path AS imagePath FROM CategoriesTable JOIN KeywordsTable ON idKeyWords = idCategories WHERE category_name = :categoryName LIMIT 1")

CategoriesTable findImagePathByKeyWordName(String categoryName);

这是正确的解决方案吗？我可以通过输入关键字来获取imagePath吗？

谢谢您的建议：）

CategoriesTable.class

@Entity
public class CategoriesTable {
@NonNull
@PrimaryKey(autoGenerate = true)
private int idCategories;

@ColumnInfo(name = "category_name")
private String categoryName;

@ColumnInfo(name = "image_path")
private String imagePath;
//getters and setters

KeywordsTable.class

@Entity
public class KeywordsTable {
@PrimaryKey(autoGenerate = true)
private int idKeyWords;

@ColumnInfo(name = "keywords_name")
private String keywordsName;
//getters and setters

Answer 1

首先，必须在关系的many端提供外键。此外，您应该在每个表的@Entity批注中设置名称。

KeywordsTable.java

@Entity(tableName = "keywords",
        foreignKeys = @ForeignKey(entity = CategoriesTable.class,
                                  parentColumns = "idCategories",
                                  childColumns = "categoryId",
                                  onDelete = CASCADE))
public class KeywordsTable {
    @PrimaryKey(autoGenerate = true)
    private int idKeyWords;

    @ColumnInfo(name = "keywords_name")
    private String keywordsName;

    private int categoryId;

    //getters and setters
}

CategoriesTable.java

@Entity(tableName = "categories")
public class CategoriesTable {
    @PrimaryKey(autoGenerate = true)
    private int idCategories;

    @ColumnInfo(name = "category_name")
    private String categoryName;

    @ColumnInfo(name = "image_path")
    private String imagePath;
    //getters and setters
}

dao接口中的方法应如下所示：

@Query("SELECT image_path FROM categories INNER JOIN keywords" +
       "ON idCategories = categoryId WHERE keywords_name = :keyword LIMIT 1")
String findImagePathByKeyWordName(String keyword);

通过提供另一个表中的字段来从表中获取字段（房间库）

1 个答案: