使用Hot Chocolate和.NET 6构建GraphQL应用(2) —— 实体相关功能实现

阅读原文时间：2022年01月28日阅读：2

在本文中，我们将会准备好用于实现GraphQL接口所依赖的底层数据，为下一篇文章具体实现GraphQL接口做准备。

实体定义

在上一篇文章使用Hot Chocolate和.NET 6构建GraphQL应用(1) —— GraphQL及示例项目介绍我们给出的实体关系图稍微进行一些简化，去掉了关于评论回复的实体定义。我们先来实现关于Post/Comment/Tag的实体以及对应的Configuration：

Post.cs

namespace PostGraphi.Domain.Post.Entities;

public class Post : AuditableEntity, IEntity, IHasDomainEvent
{
public Guid Id { get; set; }
public string? Title { get; set; }
public string? Author { get; set; }
public string? Abstraction { get; set; }
public string? Content { get; set; }
public string? Link { get; set; }
public DateTime PublishedAt { get; set; }
```
public ICollection<Tag> Tags { get; set; } = new HashSet<Tag>();
public ICollection<Comment> Comments { get; set; } = new List<Comment>();

public List<DomainEvent> DomainEvents { get; set; } = new();
```
}
Comment.cs

namespace PostGraphi.Domain.Post.Entities;

public class Comment : IEntity
{
public Guid Id { get; set; }
public string? Content { get; set; }
public string? Name { get; set; }
public DateTime CreatedAt { get; set; }
```
public Guid PostId { get; set; }
public Post Post { get; set; }
```
}
Tag.cs

namespace PostGraphi.Domain.Post.Entities;

public class Tag : IEntity
{
public Guid Id { get; set; }
public string? Name { get; set; }
```
public ICollection<Post> Posts { get; set; } = new HashSet<Post>();
```
}

PostConfiguration.cs

namespace PostGraphi.Infrastructure.Persistence.Configurations;

public class PostConfiguration : IEntityTypeConfiguration
{
public void Configure(EntityTypeBuilder builder)
{
builder.Ignore(e => e.DomainEvents);

    builder.Property(t => t.Title).HasMaxLength(200).IsRequired();builder.HasMany(t =&gt; t.Tags).WithMany(a =&gt; a.Posts);
builder.HasMany(t =&gt; t.Comments).WithOne(c =&gt; c.Post).HasForeignKey(c =&gt; c.PostId);
}

}

CommentConfiguration.cs

namespace PostGraphi.Infrastructure.Persistence.Configurations;

public class CommentConfiguration : IEntityTypeConfiguration
{
public void Configure(EntityTypeBuilder builder)
{
builder.Property(t => t.Content).HasMaxLength(255).IsRequired();
```
    builder.HasOne(t => t.Post).WithMany(a => a.Comments).HasForeignKey(t=>t.PostId);
}
```
}
TagConfiguration.cs

namespace PostGraphi.Infrastructure.Persistence.Configurations;

public class TagConfiguration : IEntityTypeConfiguration
{
public void Configure(EntityTypeBuilder builder)
{
builder.Property(t => t.Name).HasMaxLength(30).IsRequired();
```
    builder.HasMany(t => t.Posts).WithMany(a => a.Tags);
}
```
}

并在DbContext类中添加：

PostGraphiDbContext.cs

public DbSet Posts => Set();
public DbSet Tags => Set();
public DbSet Comments => Set();

数据库注入

我们需要修改模版里默认的数据库注入的方式，为了演示重点内容起见，我将数据库修改为SQLite：

InfrastructureDependencyInjections.cs

// 省略其他…
// 为了注入数据库实例时还能在构造函数中使用依赖注入
services.AddEntityFrameworkSqlite();
// 使用AddPooledDbContextFactory进行数据库的注入，因为在GraphQL的并发请求下，直接AddDbContext在执行时会报错。
services.AddPooledDbContextFactory((serviceProvider, options) =>
{
options.UseSqlite("Data Source=PostGraphi.db");
// 允许在DbContext的构造函数中使用依赖注入容器
options.UseInternalServiceProvider(serviceProvider);
});

准备种子数据

修改PostGraphiDbContextSeed内容，准备一些种子数据：

PostGraphiDbContextSeed.cs

public static async Task SeedSampleDataAsync(PostGraphiDbContext context)
{
if (!context.Posts.Any())
{
var posts = new List
{
new()
{
Title = "1 - introduction to graphql",
Abstraction = "this is an introduction post for graphql",
Content = "some random content for post 1",
Author = "code4nothing",
PublishedAt = DateTime.Now.AddDays(-2),
Link = "http://link-to-post-1.html",
Comments = new List
{
new() { CreatedAt = DateTime.Now.AddHours(-3), Content = "comment 01 for post 1", Name = "kindUser01" },
new() { CreatedAt = DateTime.Now.AddHours(-2), Content = "comment 02 for post 1", Name = "kindUser01" },
new() { CreatedAt = DateTime.Now, Content = "comment 03 for post 1", Name = "kindUser02" }
},
Tags = new List
{
new() { Name = "graphql" },
new() { Name = ".net6" }
}
},
new()
{
Title = "2 - integrate graphql with hot chocolate to .net6",
Abstraction = "this is an introduction post for how to integrate graphql to .net6",
Content = "some random content for post 2",
Author = "code4nothing",
PublishedAt = DateTime.Now.AddDays(-1),
Link = "http://link-to-post-2.html",
Comments = new List
{
new() { CreatedAt = DateTime.Now.AddHours(-5), Content = "comment 01 for post 2", Name = "kindUser02" },
new() { CreatedAt = DateTime.Now.AddHours(-1), Content = "comment 02 for post 2", Name = "kindUser03" },
new() { CreatedAt = DateTime.Now, Content = "comment 03 for post 2", Name = "kindUser04" }
},
Tags = new List
{
new() { Name = "graphql" },
new() { Name = ".net6" },
new() { Name = "hot chocolate" }
}
},
new()
{
Title = "3 - use Dapr with .net6",
Abstraction = "this is an introduction post for how to use dapr in .net6 applications",
Content = "some random content for post 3",
Author = "code4dapr",
PublishedAt = DateTime.Now.AddDays(-1),
Link = "http://link-to-post-3.html",
Comments = new List
{
new() { CreatedAt = DateTime.Now.AddHours(-3), Content = "comment 01 for post 3", Name = "kindUser01" },
new() { CreatedAt = DateTime.Now.AddHours(-2), Content = "comment 02 for post 3", Name = "kindUser02" },
new() { CreatedAt = DateTime.Now, Content = "comment 03 for post 3", Name = "kindUser04" },
new() { CreatedAt = DateTime.Now, Content = "comment 04 for post 3", Name = "kindUser03" }
},
Tags = new List
{
new() { Name = "dapr" },
new() { Name = ".net6" }
}
},
new()
{
Title = "4 - use dapr service invocation in .net6",
Abstraction = "this is an introduction post for how to use dapr service invocation in .net6",
Content = "some random content for post 4",
Author = "code4dapr",
PublishedAt = DateTime.Now.AddDays(-1),
Link = "http://link-to-post-4.html",
Comments = new List
{
new() { CreatedAt = DateTime.Now.AddHours(-3), Content = "comment 01 for post 4", Name = "kindUser04" }
},
Tags = new List
{
new() { Name = "dapr" },
new() { Name = ".net6" },
new() { Name = "service invocation" }
}
}
};
```
    context.Posts.AddRange(posts);
    await context.SaveChangesAsync();
}
```
}

应用数据库迁移和种子数据生成

Program.cs

public static void ApplyDatabaseMigration(this WebApplication app)
{
using var scope = app.Services.CreateScope();

var retryPolicy = CreateRetryPolicy(app.Configuration, Log.Logger);
// 注意因为数据库的注入方式变了，所以获取数据库Context的方法也相应修改
using var context = scope.ServiceProvider.GetRequiredService<IDbContextFactory<PostGraphiDbContext>>().CreateDbContext();
// 应用Migration
retryPolicy.Execute(context.Database.Migrate);
// 生成种子数据
PostGraphiDbContextSeed.SeedSampleDataAsync(context).Wait();

}

执行dotnet migrations add命令行去生成第一次migration数据，运行程序，可以通过数据库工具看到种子数据已经被成功生成到数据库了。

下一篇文章起，我们就开始使用Hot Chocolate来完成GraphQL接口的实现。在进入之前，我想先简单介绍一下在Hot Chocolate中编写GraphQL相关功能的三种方式，为下一节内容作准备：