android - ORM Lite 在创建包含多级外键的表时抛出错误

Question

创建表 ActivityLog 时，我在 ORM Lite 上遇到此错误:

10-23 04:06:32.255: E/com.timelord.dao.DatabaseHelper(1487): 
Caused by: java.sql.SQLException: ORMLite can't store unknown class class 
com.timelord.pojo.Category for field 'category'. Serializable fields must 
specify dataType=DataType.SERIALIZABLE

我怀疑是多级外键导致的。从下面的POJO类可以看出，ActivityLog有Activity，Activity有Category。

Activity 和 Category 工作正常。

知道如何进行正确的映射吗？

@DatabaseTable(tableName = "activityLogs")
public class AcitvityLog implements Serializable {

    private static final long serialVersionUID = 1L;

    @DatabaseField(generatedId = true)
    private int id;

    @DatabaseField(canBeNull = false)
    @DatabaseFieldForeign(foreign = true)
    private Activity activity;

    @DatabaseField(dataType = DataType.DATE, canBeNull = false)
    private Timestamp start;

    @DatabaseField(dataType = DataType.DATE, canBeNull = true)
    private Timestamp end;
}

@DatabaseTable(tableName = "activities")
public class Activity extends BaseEntity implements Serializable {

    private static final long serialVersionUID = 1L;

    @DatabaseField(canBeNull = false)
    @DatabaseFieldForeign(foreign = true)
    private Category category;
}

@DatabaseTable(tableName = "categories")
public class Category extends BaseEntity implements Serializable {

    private static final long serialVersionUID = 1L;
}

public class BaseEntity {
    @DatabaseField(generatedId = true)
    private Integer id;

    @DatabaseField(canBeNull = false)
    private String name;
}

Answer 1

不，ORMLite可以毫无问题地处理多级外键。问题是您不能混合使用 @DatabaseField 和 @DatabaseFieldForeign 注释。你想要的是:

@DatabaseField(canBeNull = false, foreign = true)
private Activity activity;

或者，如果您想使用在 Android 下运行速度更快的较小注解:

@DatabaseFieldSimple(canBeNull = false)
@DatabaseFieldForeign(foreign = true)

只是@DatabaseField 或@DatabaseFieldSimple 和其他@DatabaseField... 注释.以下是 @DatabaseFieldSimple 的文档:

http://ormlite.com/javadoc/ormlite-core/com/j256/ormlite/field/DatabaseFieldSimple.html