用ef core 3.1翻译创建的用户名的最佳方法是什么

Question

public class Entity
{
public string Id { get; set; }
public string CreatedBy { get; set; }
public string LastUpdatedBy { get; set; }
[NotMapped]
public string Creator { get; set; }
[NotMapped]
public string Updater { get; set; }
}
public class User
{
public string Name { get; set; }
public string Id { get; set; }
}

我将搜索实体，用ef核心查询对Creator/Updater属性进行排序(并返回UserInfo.Name(，知道吗？

Answer 1

经过数小时的研究，指

如何使用linq扩展方法执行左外部联接

实体框架联接3个表

订单中有三种方式(前者优先于后者(：

class Program
{
static void Main()
{
using TenantDBContext dbContext = new TenantDBContext("PORT=5432;DATABASE=linqtosql;HOST=xxx.com;PASSWORD=xxx;USER ID=postgres;Pooling=true;Minimum Pool Size=10;Application Name=xxx");
var result = (
from entity in dbContext.Entities
join user in dbContext.Users on entity.CreatedBy equals user.Id into temp1
from ce in temp1.DefaultIfEmpty()
join user1 in dbContext.Users on entity.UpdatedBy equals user1.Id into temp2
from cu in temp2.DefaultIfEmpty()
select new Entity() { Id = entity.Id, CreatedBy = entity.CreatedBy, UpdatedBy = entity.UpdatedBy, Creator = ce.Name, Updater = ce.Name }
).ToList();
Console.WriteLine(JsonConvert.SerializeObject(result, Formatting.Indented));
var result2 = dbContext.Entities
.GroupJoin(dbContext.Users, e => e.CreatedBy, u => u.Id, (e, u) => new { Entity = e, User = u })
.SelectMany(eUser => eUser.User.DefaultIfEmpty(), (e, u) => new Entity() { Id = e.Entity.Id, CreatedBy = e.Entity.CreatedBy, UpdatedBy = e.Entity.UpdatedBy, Creator = u.Name })
.GroupJoin(dbContext.Users, e => e.UpdatedBy, u => u.Id, (e, u) => new { Entity = e, User = u })
.SelectMany(eUser => eUser.User.DefaultIfEmpty(), (e, u) => new Entity() { Id = e.Entity.Id, CreatedBy = e.Entity.CreatedBy, UpdatedBy = e.Entity.UpdatedBy, Creator = e.Entity.Creator, Updater = u.Name }
).ToList();
Console.WriteLine(JsonConvert.SerializeObject(result2, Formatting.Indented));
var result3 = dbContext.Entities
.SelectMany(entity => dbContext.Users.Where(user => entity.CreatedBy == user.Id).DefaultIfEmpty(), (entity, user) => new { Entity = entity, User = user })
.SelectMany(entity => dbContext.Users.Where(user => entity.Entity.UpdatedBy == user.Id).DefaultIfEmpty(), (entity, user) => new Entity { Id = entity.Entity.Id, CreatedBy = entity.Entity.CreatedBy, UpdatedBy = entity.Entity.UpdatedBy, Creator = entity.User.Name, Updater = user.Name })
.ToList();
Console.WriteLine(JsonConvert.SerializeObject(result2, Formatting.Indented));
}
}