SQLite-Net扩展| 相同实体的外键引用

Question

I am facing an issue in using SQLite-Net Extensions to save data in local DB in scenario where the foreign key is referencing the same entity (self-join).

Example – Employee and Manager. Every employee has a manager and a manager is also an employee. I am facing issues in saving data in such cases. It will be really helpful if you can provide some insights. Does this extension support this kind of relationship?

Answer 1

Yes, relationships between objects of the same class are supported, but the foreign keys and inverse properties must be explicitly specified in the relationship property attribute because the discovery system will get it wrong as there are be two relationships with the same type.

This example is extracted from the project readme:

public class TwitterUser {
    [PrimaryKey, AutoIncrement]
    public int Id { get; set; }

    public string Name { get; set; }

    [ManyToMany(typeof(FollowerLeaderRelationshipTable), "LeaderId", "Followers",
        CascadeOperations = CascadeOperation.CascadeRead)]
    public List<TwitterUser> FollowingUsers { get; set; }

    // ReadOnly is required because we're not specifying the followers manually, but want to obtain them from database
    [ManyToMany(typeof(FollowerLeaderRelationshipTable), "FollowerId", "FollowingUsers",
        CascadeOperations = CascadeOperation.CascadeRead, ReadOnly = true)]
    public List<TwitterUser> Followers { get; set; }
}

// Intermediate class, not used directly anywhere in the code, only in ManyToMany attributes and table creation
public class FollowerLeaderRelationshipTable {
    public int LeaderId { get; set; }
    public int FollowerId { get; set; }
}

As you can see here we have a many-to-many between Twitter users. In your case it will be a one-to-many, so you won't need the intermediate table and you'll need the foreign key ( ManagerId for example) in your Person class.