Xamarin形成SQLite关系 [英] Xamarin forms SQLite relation

问题描述

我现在确实已经搜索了一段时间，但是找不到并理解它是如何工作的.我将以Xamarin形式创建一个应用程序，并从SQLite开始.我需要为应用程序中的每个主要项目都具有唯一的列表项.

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.

例如，我有一个包含物品的列表.当我在列表中选择一个项目时，将弹出一个新页面并显示该项目的项目.

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.

因此，从我的角度来看，我需要两个具有相互关系的SQLite表.

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

这是包含所有配置文件的主表

[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; }

}

这是每个配置文件的logg表，对于每个配置文件应该是唯一的

[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; }
}

添加类似的项目

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);
    }
}

Logg和Profile列表/表都可以工作，但是两者之间没有任何关系，因此Logg在所有Profile中都显示相同的内容.

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.

请帮助我该怎么做.

非常感谢.

推荐答案

如何使用Linq并加入关系.
1 .- .首先，您必须添加名称空间:

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

using System.Linq;

2 .- .将ProfileItems类中的属性更改为 IEnumerable

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

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

3 .- .这是将Logg与配置文件项结合在一起的方法.

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
    };

这篇关于Xamarin形成SQLite关系的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！