EF Core一对多关系配置

  • 创建文章、评论实体类 ```csharp using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks;

namespace EFCoreRelation.Models { public class Article { public long ID { get; set; } public string Title { get; set; } public string Content { get; set; }

  1.     public List<Comment> Comments { get; set; } = new List<Comment>();
  2. }

}

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks;

namespace EFCoreRelation.Models { public class Comment { public long ID { get; set; } 

  1.     public string Message { get; set; }
  3.     public Article Article { get; set; }
  4. }

}

  2. - 安装Nuget包
  4. Microsoft.EntityFrameworkCore.SqlServer<br />Microsoft.EntityFrameworkCore.Tools
  6. - 创建配置类，实现一对多的外键配置，下面尤其要注意评论配置类。
  8. **多个评论有一篇文章（HasOne<Article>(c=>c.Article)，一篇文章拥有多个评论(WithMany<Comment>(a=>a.Comments))**
  9. ```csharp
  10. using EFCoreRelation.Models;
  11. using Microsoft.EntityFrameworkCore;
  12. using System;
  13. using System.Collections.Generic;
  14. using System.Linq;
  15. using System.Text;
  16. using System.Threading.Tasks;
  18. namespace EFCoreRelation.Configs
  19. {
  20.     public class ArticleConfig : IEntityTypeConfiguration<Article>
  21.     {
  22.         public void Configure(Microsoft.EntityFrameworkCore.Metadata.Builders.EntityTypeBuilder<Article> builder)
  23.         {
  24.             builder.ToTable("T_Article");
  25.             builder.Property(a => a.Content).IsRequired();
  26.             builder.Property(a => a.Title).IsRequired().IsUnicode().HasMaxLength(255);
  27.         }
  28.     }
  29. }
  32. using EFCoreRelation.Models;
  33. using Microsoft.EntityFrameworkCore;
  34. using System;
  35. using System.Collections.Generic;
  36. using System.Linq;
  37. using System.Text;
  38. using System.Threading.Tasks;
  40. namespace EFCoreRelation.Configs
  41. {
  42.     public class CommentConfig : IEntityTypeConfiguration<Comment>
  43.     {
  44.         public void Configure(Microsoft.EntityFrameworkCore.Metadata.Builders.EntityTypeBuilder<Comment> builder)
  45.         {
  46.             builder.ToTable("T_Comment");
  47.             builder.Property(c => c.Message).IsRequired().IsUnicode();
  48.             builder.HasOne<Article>(c => c.Article).WithMany(a => a.Comments).IsRequired();
  49.         }
  50.     }
  51. }
  • 创建AlbertDbContext ```csharp using EFCoreRelation.Models; using Microsoft.EntityFrameworkCore; using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks;

namespace EFCoreRelation.DbContexts { public class AlbertDbContext:DbContext { public DbSet

? Articles { get; set; } public DbSet? Comment { get; set; }

  1.     protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
  2.     {
  3.         optionsBuilder.UseSqlServer(connectionString: "Server=.;Database=Albertefcore;" +
  4.             "Trusted_Connection=True;MultipleActiveResultSets=true");
  5.     }
  7.     protected override void OnModelCreating(ModelBuilder modelBuilder)
  8.     {
  9.         base.OnModelCreating(modelBuilder);
  10.         modelBuilder.ApplyConfigurationsFromAssembly(this.GetType().Assembly);
  11.     }      
  12. }

}

  2. - 执行数据库迁移
  3. ```csharp
  4. Add-Migration "Init SQLServer"
  5. Update-Database
  • 查看数据库是否有数据（如果配置正常则已有数据）
  • 向数据库中插入值 ```csharp using EFCoreRelation.DbContexts; using EFCoreRelation.Models; using Microsoft.EntityFrameworkCore;

// 插入值 //Article article = new Article(); //article.Title = “微软.NET最新动态”; //article.Content = “微软发布了最新的.NET7 Preview版本，该版本优化了JWT配置”; //Comment comment1 = new Comment() { Message = “真的好棒” }; //Comment comment2 = new Comment() { Message = “终于优化了JWT了” }; //Comment comment3 = new Comment() { Message = “拥抱开源后微软变得很牛” }; //Comment comment4 = new Comment() { Message = “巨硬无敌” }; //article.Comments.Add(comment1); //article.Comments.Add(comment2); //article.Comments.Add(comment3); //article.Comments.Add(comment4); //using var ctx = new AlbertDbContext(); //ctx.Articles.Add(article); //await ctx.SaveChangesAsync();

// 移除全部数据 //using var ctx = new AlbertDbContext();

//foreach (var item in ctx.Articles) //{ // ctx.Articles.Remove(item); //} //ctx.SaveChanges();

// 注意SingleOrDefault返回空值的情况 using var ctx = new AlbertDbContext(); try { var articlesingle = ctx.Articles.Include(a => a.Comments).SingleOrDefault(c => c.ID == 4); foreach (var item in articlesingle.Comments) { Console.WriteLine(item.Message); }

} catch (Exception ex) { throw ex; }

```