C# 具有多个表的Linq查询
尝试键入将包含两个表中信息的Linq表达式C# 具有多个表的Linq查询,c#,linq,asp.net-mvc-4,C#,Linq,Asp.net Mvc 4,尝试键入将包含两个表中信息的Linq表达式 var articles = db.Articles; var articlescores = db.ArticleScores; articles表具有标题字段 articles.title articlescores表具有Actuality字段和ArticleID字段 articlescores.ActualCity artickescores.ArticleID (which links to articles
var articles = db.Articles;
var articlescores = db.ArticleScores;
articles.title
articlescores.ActualCity
artickescores.ArticleID (which links to articles table)
.Count（）articlescores.actualityarticles.title一起存储在字符串中
基本上，一个城市浏览的文章最多
样本数据：
ArticleScore表：
ID articleID City (Note: articleID is not dependent on City, I just wrote it this way)
1 1 New York
2 2 Boston
3 1 New York
4 1 New York
5 1 New York
6 2 Boston
条款表：
ID title
1 TitleOneOfArticles
2 TitleTwoOfArticles
预期产出（因为纽约有4个，波士顿只有2个）：
只需要一行输出。试试这个linq：
db.Articles
.Join(db.ArticleScores ,
art=> art.ID,
scr=> scr.ID,
(art, scr) => new { article= art, score= scr})
.Where(both => (both.art.ID == cityID))
.Select(both => both.score)
cityId是您应该发送的参数您的问题是自相矛盾的，而且它还缺少一些关键信息。所以我要猜一猜
- 你没有提到你正在使用的linq。您正在使用实体框架吗？光速？还有别的吗？我假设它是实体框架
- 你说你基本上需要一个城市浏览最多的文章，但接着你给出了一些不同的例子。我想这是《城市》杂志上浏览量最大的一篇文章
- 您说articleID不依赖于城市，但接下来给出了一个城市和articleID之间一对一关系的示例
以下是我如何理解ArticleScore示例数据集：
ID articleID City
? 1 New York
? 1 New York
? 1 New York
? 1 Boston
? 2 New York
? 2 Boston
? 2 Boston
在该数据集中，纽约的第1条有3个视图，第2条有1个视图。同样，在波士顿，第2条有两种观点，第1条有一种观点
根据这些数据，我假设你想得到这样的东西
TitleTwoOfArticles, Boston(2)
TitleOneOfArticles, NewYork(3)
上表表明，波士顿最受欢迎的文章是第2条，共有2篇。在纽约，浏览量最大的文章是1篇，总共有3篇。请注意，此处未显示一篇文章在所有城市的浏览总数
A创建了一个代码示例来测试上述场景，我使用了：
- Visual Studio 2013/.net 4.5
- 实体框架6
代码如下：
using System;
using System.Collections.Generic;
using System.Linq;
using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Entity;
using System.Data.Entity.ModelConfiguration;
namespace SO22928136
{
public interface IMyDbContext : IDisposable
{
IDbSet<Article> Articles { get; set; }
IDbSet<ArticleScore> ArticleScores { get; set; }
int SaveChanges();
}
public class MyDbContext : DbContext, IMyDbContext
{
public IDbSet<Article> Articles { get; set; }
public IDbSet<ArticleScore> ArticleScores { get; set; }
static MyDbContext()
{
Database.SetInitializer(new DropCreateDatabaseAlways<MyDbContext>());
}
public MyDbContext(string connectionString) : base(connectionString)
{
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Configurations.Add(new ArticleConfiguration());
modelBuilder.Configurations.Add(new ArticleScoreConfiguration());
}
}
public class Article
{
public int Id { get; set; }
public string Title { get; set; }
public virtual ICollection<ArticleScore> ArticleScores { get; set; }
public Article()
{
ArticleScores = new List<ArticleScore>();
}
}
public class ArticleScore
{
public int Id { get; set; }
public int ArticleId { get; set; }
public string ActualCity { get; set; }
public virtual Article Article { get; set; }
}
internal class ArticleConfiguration : EntityTypeConfiguration<Article>
{
public ArticleConfiguration()
{
ToTable("Article");
HasKey(x => x.Id);
Property(x => x.Id).HasColumnName("Id").IsRequired().HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
Property(x => x.Title).HasColumnName("Title").IsOptional();
}
}
internal class ArticleScoreConfiguration : EntityTypeConfiguration<ArticleScore>
{
public ArticleScoreConfiguration()
{
ToTable("ArticleScore");
HasKey(x => x.Id);
Property(x => x.Id).HasColumnName("Id").IsRequired().HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
Property(x => x.ArticleId).HasColumnName("ArticleId").IsRequired();
Property(x => x.ActualCity).HasColumnName("ActualCity").IsOptional().HasMaxLength(10);
HasRequired(a => a.Article).WithMany(b => b.ArticleScores).HasForeignKey(c => c.ArticleId);
}
}
class Program
{
static void Main()
{
MyDbContext context = new MyDbContext("Data Source=(local);Initial Catalog=SO22928136;Integrated Security=True;");
CreateTestData(context);
var countOfArticlesPerCity = context.ArticleScores.GroupBy(s => new {s.ArticleId, s.ActualCity}).Select(g => new {g.Key.ArticleId, g.Key.ActualCity, Count = g.Count()});
var highestArticleCountPerCity = countOfArticlesPerCity.GroupBy(x => x.ActualCity).Select(g => g.OrderByDescending(x => x.Count).FirstOrDefault());
var highestArticleCountPerCityWithArticleTitle = context.Articles.Join(highestArticleCountPerCity, x => x.Id, p => p.ArticleId, (x, p) => new { x.Title, p.ActualCity, p.Count });
foreach (var line in highestArticleCountPerCityWithArticleTitle)
{
Console.WriteLine("{0}, {1}({2})",line.Title,line.ActualCity, line.Count);
}
}
private static void CreateTestData(MyDbContext context)
{
Article articleOne = new Article { Title = "TitleOneOfArticles" };
Article articleTwo = new Article { Title = "TitleTwoOfArticles" };
articleOne.ArticleScores.Add(new ArticleScore { ActualCity = "NewYork" });
articleOne.ArticleScores.Add(new ArticleScore { ActualCity = "NewYork" });
articleOne.ArticleScores.Add(new ArticleScore { ActualCity = "NewYork" });
articleOne.ArticleScores.Add(new ArticleScore { ActualCity = "Boston" });
articleTwo.ArticleScores.Add(new ArticleScore { ActualCity = "NewYork" });
articleTwo.ArticleScores.Add(new ArticleScore { ActualCity = "Boston" });
articleTwo.ArticleScores.Add(new ArticleScore { ActualCity = "Boston" });
context.Articles.Add(articleOne);
context.Articles.Add(articleTwo);
context.SaveChanges();
}
}
}
使用系统；
使用System.Collections.Generic；
使用System.Linq；
使用System.ComponentModel.DataAnnotations.Schema；
使用System.Data.Entity；
使用System.Data.Entity.ModelConfiguration；
名称空间SO22928136
{
公共接口IMyDbContext:IDisposable
{
IDbSet项目{get；set；}
IDbSet属性{get；set；}
int SaveChanges（）；
}
公共类MyDbContext:DbContext，IMyDbContext
{
公共IDbSet项目{get；set；}
公共IDbSet属性{get；set；}
静态MyDbContext（）
{
SetInitializer（新的DropCreateDatabaseAlways（））；
}
公共MyDbContext（string connectionString）：基本（connectionString）
{
}
模型创建时受保护的覆盖无效（DbModelBuilder modelBuilder）
{
基于模型创建（modelBuilder）；
modelBuilder.Configurations.Add（newarticleconfiguration（））；
添加（新的ArticleScoreConfiguration（））；
}
}
公共类文章
{
公共int Id{get；set；}
公共字符串标题{get；set；}
公共虚拟ICollection{get；set；}
公共物品（）
{
ArticleScores=新列表（）；
}
}
公开课文章分数
{
公共int Id{get；set；}
公共int ArticleId{get；set；}
公共字符串实际值{get；set；}
公共虚拟项目{get；set；}
}
内部类ArticleConfiguration:EntityTypeConfiguration
{
公共配置（）
{
可折叠（“物品”）；
HasKey（x=>x.Id）；
属性（x=>x.Id）.HasColumnName（“Id”）.IsRequired（）.hasDatabaseGenerateOption（DatabaseGenerateOption.Identity）；
属性（x=>x.Title）.HasColumnName（“Title”）.IsOptional（）；
}
}
内部类ArticleScoreConfiguration:EntityTypeConfiguration
{
公共配置（）
{
ToTable（“ArticleScore”）；
HasKey（x=>x.Id）；
属性（x=>x.Id）.HasColumnName（“Id”）.IsRequired（）.hasDatabaseGenerateOption（DatabaseGenerateOption.Identity）；
属性（x=>x.ArticleId）.HasColumnName（“ArticleId”）.IsRequired（）；
属性（x=>x.ActualCity）.HasColumnName（“ActualCity”）.IsOptional（）.HasMaxLength（10）；
HasRequired（a=>a.Article）。有许多（b=>b.Article分数）。HasForeignKey（c=>c.ArticleId）；
}
}
班级计划
{
静态void Main（）
{
MyDbContext上下文=新的MyDbContext（“数据源=（本地）；初始目录=SO22928136；集成安全性=True；”）；
CreateTestData（上下文）；
var countOfArticlesPerCity=context.ArticleScores.GroupBy（s=>new{s.ArticleId，s.ActualCity}）。选择（g=>new{g.Key.ArticleId，g.Key.ActualCity，Count=g.Count（）；
var highestarticlecontpercity=countOfArticlesPerCity.GroupBy（x=>x.ActualCity）。选择（g=>g.OrderByDescending（x=>x.Count）。FirstOrDefault（）；
var highestArticleCountPerCityWithArticleTitle=context.Articles.Join（highestArticleCountPerCity，x=>x.Id，p=>p.ArticleId，（x，p）=>new{x.Title，p.ActualCity，p.Count}）；
foreach（highestArticleCountPerCityWithArticleTitle中的var行）
{
WriteLine（“{0}，{1}（{2}）”，line.Title，line.ActualCity，line.Count）；
}
}
私有静态void CreateTestData（MyDbContext上下文）
{
第1条=新的第{Title=“TitleOneOfArticles”}；
第2条=新的第{Title=“TitleTwoOfArticles”}；
articleOne.ArticleScores.Add（新ArticleScores{ActualCity=“NewYork”}）；
文章
using System;
using System.Collections.Generic;
using System.Linq;
using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Entity;
using System.Data.Entity.ModelConfiguration;
namespace SO22928136
{
public interface IMyDbContext : IDisposable
{
IDbSet<Article> Articles { get; set; }
IDbSet<ArticleScore> ArticleScores { get; set; }
int SaveChanges();
}
public class MyDbContext : DbContext, IMyDbContext
{
public IDbSet<Article> Articles { get; set; }
public IDbSet<ArticleScore> ArticleScores { get; set; }
static MyDbContext()
{
Database.SetInitializer(new DropCreateDatabaseAlways<MyDbContext>());
}
public MyDbContext(string connectionString) : base(connectionString)
{
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Configurations.Add(new ArticleConfiguration());
modelBuilder.Configurations.Add(new ArticleScoreConfiguration());
}
}
public class Article
{
public int Id { get; set; }
public string Title { get; set; }
public virtual ICollection<ArticleScore> ArticleScores { get; set; }
public Article()
{
ArticleScores = new List<ArticleScore>();
}
}
public class ArticleScore
{
public int Id { get; set; }
public int ArticleId { get; set; }
public string ActualCity { get; set; }
public virtual Article Article { get; set; }
}
internal class ArticleConfiguration : EntityTypeConfiguration<Article>
{
public ArticleConfiguration()
{
ToTable("Article");
HasKey(x => x.Id);
Property(x => x.Id).HasColumnName("Id").IsRequired().HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
Property(x => x.Title).HasColumnName("Title").IsOptional();
}
}
internal class ArticleScoreConfiguration : EntityTypeConfiguration<ArticleScore>
{
public ArticleScoreConfiguration()
{
ToTable("ArticleScore");
HasKey(x => x.Id);
Property(x => x.Id).HasColumnName("Id").IsRequired().HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
Property(x => x.ArticleId).HasColumnName("ArticleId").IsRequired();
Property(x => x.ActualCity).HasColumnName("ActualCity").IsOptional().HasMaxLength(10);
HasRequired(a => a.Article).WithMany(b => b.ArticleScores).HasForeignKey(c => c.ArticleId);
}
}
class Program
{
static void Main()
{
MyDbContext context = new MyDbContext("Data Source=(local);Initial Catalog=SO22928136;Integrated Security=True;");
CreateTestData(context);
var countOfArticlesPerCity = context.ArticleScores.GroupBy(s => new {s.ArticleId, s.ActualCity}).Select(g => new {g.Key.ArticleId, g.Key.ActualCity, Count = g.Count()});
var highestArticleCountPerCity = countOfArticlesPerCity.GroupBy(x => x.ActualCity).Select(g => g.OrderByDescending(x => x.Count).FirstOrDefault());
var highestArticleCountPerCityWithArticleTitle = context.Articles.Join(highestArticleCountPerCity, x => x.Id, p => p.ArticleId, (x, p) => new { x.Title, p.ActualCity, p.Count });
foreach (var line in highestArticleCountPerCityWithArticleTitle)
{
Console.WriteLine("{0}, {1}({2})",line.Title,line.ActualCity, line.Count);
}
}
private static void CreateTestData(MyDbContext context)
{
Article articleOne = new Article { Title = "TitleOneOfArticles" };
Article articleTwo = new Article { Title = "TitleTwoOfArticles" };
articleOne.ArticleScores.Add(new ArticleScore { ActualCity = "NewYork" });
articleOne.ArticleScores.Add(new ArticleScore { ActualCity = "NewYork" });
articleOne.ArticleScores.Add(new ArticleScore { ActualCity = "NewYork" });
articleOne.ArticleScores.Add(new ArticleScore { ActualCity = "Boston" });
articleTwo.ArticleScores.Add(new ArticleScore { ActualCity = "NewYork" });
articleTwo.ArticleScores.Add(new ArticleScore { ActualCity = "Boston" });
articleTwo.ArticleScores.Add(new ArticleScore { ActualCity = "Boston" });
context.Articles.Add(articleOne);
context.Articles.Add(articleTwo);
context.SaveChanges();
}
}
}