SQLite.NET扩展多对多，没有创建连接表记录

Question

我是使用SQLite.NET和扩展的新手。

为了我的最佳能力，我遵循了我找到的指南，但在多对多连接表中没有创建记录，我不知道为什么。

我有一个解决方案NuGet依赖于SQLiteNetExtensions项目。

我有以下表格：

[Table("Contact")] 
public class Contact 
{ 
    [PrimaryKey, AutoIncrement] 
    public int Id { get; set; } 

    [MaxLength(50)] 
    public string FirstName { get; set; } 

    [MaxLength(50)] 
    public string Surname { get; set; } 

    [ManyToMany(typeof(Participant))] 
    public List<Journey> Journeys { get; set; } 
} 

[Table("Journey")] 
public class Journey 
{ 
    [PrimaryKey, AutoIncrement] 
    public int Id { get; set; } 

    [ManyToMany(typeof(Participant))] 
    public List<Contact> Contacts { get; set; } 

    [ManyToMany(typeof(Waypoint))] 
    public List<Location> Locations { get; set; } 
} 

[Table("Location")] 
public class Location 
{ 
    [PrimaryKey, AutoIncrement] 
    public int Id { get; set; } 

    [MaxLength(50)] 
    public string Name { get; set; } 

    public double Latitude { get; set; } 

    public double Longitude { get; set; } 

    [ManyToMany(typeof(Waypoint))] 
    public List<Journey> Journeys{ get; set; } 
} 

public class Participant 
{ 
    [ForeignKey(typeof(Contact))] 
    public int ContactId { get; set; } 

    [ForeignKey(typeof(Journey))] 
    public int JourneyId { get; set; } 
} 

public class Waypoint 
{ 
    [ForeignKey(typeof(Location))] 
    public int LocationId { get; set; } 

    [ForeignKey(typeof(Journey))] 
    public int JourneyId { get; set; } 
} 

当我建我用下面的测试代码数据库：

string dbPath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Personal), "xandroid.db3"); 

var db = new SQLiteConnection(platform, dbPath); 

db.DropTable<Location>(); 
db.DropTable<Waypoint>(); 
db.DropTable<Contact>(); 
db.DropTable<Participant>(); 
db.DropTable<Journey>(); 

db.CreateTable<Location>(); 
db.CreateTable<Waypoint>(); 
db.CreateTable<Contact>(); 
db.CreateTable<Participant>(); 
db.CreateTable<Journey>(); 

Location home = new Location { Name = "Home", Latitude=22.22, Longitude=22.22 }; 
Location perth = new Location { Name = "Perth", Latitude = 4444.4444, Longitude = 4444.4444 }; 
db.InsertAll(new List<Location> { home, perth }); 

Contact beans = new Contact { FirstName = "Beans", Surname = "Connor" }; 
Contact winston = new Contact { FirstName = "Winston", Surname = "Connor" }; 
db.InsertAll(new List<Contact> { beans, winston }); 

Journey travelToPerth = new Journey { Locations = new List<Location> { perth }, Contacts = new List<Contact> { beans, winston }}; 
Journey returnHome = new Journey { Locations = new List<Location> { home }, Contacts = new List<Contact> { beans, winston}}; 
db.InsertAll(new List<Journey> { travelToPerth, returnHome }); 

当我进入我用下面的代码中的数据：

var waypoints = db.Table<Waypoint>(); 
Console.Out.WriteLine(waypoints.Count() + " recorded waypoints"); 

var participants = db.Table<Participant>(); 
Console.Out.WriteLine(participants.Count() + " recorded participants"); 

var journeys = db.Table<Journey>(); 
Console.Out.WriteLine(journeys.Count() + " recorded journeys"); 

其输出为：

0 recorded waypoints 
0 recorded participants 
2 recorded journeys 

Answer 1

您正在使用普通的sqlite.net方法插入对象，这些方法对您的关系一无所知。要保存和加载关系，您必须使用SQLite-Net扩展方法。大多数的SQLite净方法也有一个WithChildren替代节省关系：

import SQLiteNetExtensions.Extensions; 

db.InsertAllWithChildren(new List<Journey> { travelToPerth, returnHome }); 

将插入这两个元素插入所需的记录，以Participant和Waypoint表保存的关系。

注意：这仍然需要Location和Contact元素已被插入到数据库中。要递归插入对象，请查看级联操作部分的SQLite-Net Extensions documentation。