Xamarin forms SQLite relation

问题

I have really been searching around for a while now but cannot find and understand how this do work. I am going to create an app in Xamarin forms and starting with SQLite. I need to have unique list items for each Main item in the app.

For example, I am having a list with items. When I am selecting an item in the list a new page will pop up and display the items of that item.

So from my point of view I am in need of two SQLite tables with relations between.

This is the Main table with all profiles

[Table("Profiles")]
public class ProfileItems
{
    [PrimaryKey, AutoIncrement]
    public int Id { get; set; }
    public string ProfileName { get; set; }
    public string ProfileRace { get; set; }
    public string iconn = "icon.png";
    public string ProfileIcon { get; set; }
    public DateTime BDay { get; set; }

    [OneToMany(CascadeOperations = CascadeOperation.All)]
    public List<LoggItems> Loggs { get; set; }

}

This is the logg table for each Profile, which should be unique for each profile

[Table("Loggs")]
public class LoggItems
{
    [PrimaryKey, AutoIncrement]

    public int Id { get; set; }
    public string Title { get; set; }
    public string Text { get; set; }

    [ForeignKey(typeof(ProfileItems))]
    public int ProfileId { get; set; }
}

Adding the items like this

public class ProfileDatabase
{

    readonly SQLiteAsyncConnection database;

    public ProfileDatabase(string dbPath)
    {
        database = new SQLiteAsyncConnection(dbPath);
        database.CreateTableAsync<ProfileItems>().Wait();
        database.CreateTableAsync<LoggItems>().Wait();
    }


    //Profile
    public Task<List<ProfileItems>> GetProfileAsync()
    {
        return database.Table<ProfileItems>().ToListAsync();
    }

    public Task<ProfileItems> GetProfileAsync(int id)
    {
        return database.Table<ProfileItems>().Where(i => i.Id == id).FirstOrDefaultAsync();
    }

    public Task<int> SaveProfileAsync(ProfileItems profileItems)
    {
        if (profileItems.Id != 0)
        {
            return database.UpdateAsync(profileItems);
        }
        else
        {
            return database.InsertAsync(profileItems);
        }
    }

    public  Task<int> DeleteProfileAsync(ProfileItems profileItems)
    {
        return database.DeleteAsync(profileItems);
    }


    //Logg
    public Task<List<LoggItems>> GetLoggAsync()
    {
        return database.Table<LoggItems>().ToListAsync();
    }

    public Task<LoggItems> GetLoggAsync(int id)
    {
        return database.Table<LoggItems>().Where(i => i.Id == id).FirstOrDefaultAsync();
    }

    public Task<int> SaveLoggAsync(LoggItems loggItems)
    {
        if (loggItems.Id != 0)
        {
            return database.UpdateAsync(loggItems);
        }
        else
        {
            return database.InsertAsync(loggItems);
        }
    }

    public Task<int> DeleteLoggAsync(LoggItems loggItems)
    {
        return database.DeleteAsync(loggItems);
    }
}

Both Logg and Profile list/tables do work but they do not have any relations between so the loggs show the same in all profile.

Please help me how I should do this.

Thanks in advanced.

回答1:

How about to use Linq and join the relationships.
1.- First you have to add the namespace:

using System.Linq;

2.- Change the property in the class ProfileItems to be a IEnumerable

[OneToMany(CascadeOperations = CascadeOperation.All)]
public virtual IEnumerable<LoggItems> Loggs { get; set; }

3.- This is the method to join the loggs with the profile items.

var profiles = await GetProfileAsync();
var loggs = await GetLoggAsync();
var query = from p in profiles
    join l in loggs on p.Id equals l.ProfileId into list
    select new ProfileItems
    {
        Id = p.Id,
        ProfileIcon = p.ProfileIcon,
        ProfileName = p.ProfileName,
        ProfileRace = p.ProfileRace,
        BDay = p.BDay,
        Loggs = list
    };

回答2:

I think you must add "virtual" keyword for enabling lazy loading.

[OneToMany(CascadeOperations = CascadeOperation.All)]
public virtual List<LoggItems> Loggs { get; set; }

And there's the "[InverseProperty]" to specify their related navigation property.

public class LoggItems
{
     *
     [ForeignKey(typeof(ProfileItems))]
     [InverseProperty("Loggs")]
     public int ProfileId { get; set; }
     *
}

来源：https://stackoverflow.com/questions/50802032/xamarin-forms-sqlite-relation