通过从另一个 table（房间图书馆）提供字段来从 table 获取字段

Question

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

我有 @Dao 界面，我做了类似

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？我会通过提供关键字来获取 imagePath 吗？

谢谢指教:)

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，您必须在关系的 many 端提供外键。此外，您应该在 @Entity 注释中设置每个 table 的名称。

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 接口中的方法应该如下所示：

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

通过从另一个 table（房间图书馆）提供字段来从 table 获取字段

Get field from table by giving field from another table (Room Library)

database

android

android-room