c# - GraphQL 并行异步查询 c# EF Core 3.0

Question

我正在尝试使用 2 个(或更多)异步子查询执行查询。遗憾的是，这是不可能的，因为 DbContext 一次只能处理 1 个请求。

项目正在使用:

• Entity Framework 3
• Graphql 3.0.0

错误

A second operation started on this context before a previous operation completed. This is usually caused by different threads using the same instance of DbContext.

类型:

Field<ListGraphType<A>>()
    .Name("A")
    .Description("query of A")
    .ResolveAsync(async context =>
        await repro.GetAllAAsync(context)
);

Field<ListGraphType<A>>()
            .Name("B")
            .Description("query of B")
            .ResolveAsync(async context =>
                await repro.GetAllBAsync(context)
            );

查询:

query {
  A {
    id
  }
  B {
    id
  }
}

DbContextPool 没有解决问题，我不想使用 StructureMap。

有没有优雅的使用方式

• 每个子查询有多个 dbContext
• 等到 dbContext 空闲

Answer 1

我最近创建了一个解决 EF 并行执行问题的项目。你可以在这里看到实现

https://github.com/fenomeno83/graphql-dotnet-globalization-demo

特别是，这里有一个查询示例，您可以找到:

public class TestGroupQueries : ObjectGraphType
{
    public TestGroupQueries(IHttpContextAccessor _httpContextAccessor)
    {
        Name = "testQueries";

        FieldAsync<TestResponseType>(
            "demoQuery",
                arguments: new QueryArguments(new QueryArgument<NonNullGraphType<IntGraphType>> { Name = "input" }),
                resolve: async context =>
                {
                    //extension method that creates scope (IServiceScope) from IServiceProvider
                    using (var scope = _httpContextAccessor.CreateScope())
                    {
                       
                        //call DemoQuery method of TestService; GetService is an extension method that use GetRequiredService from scope serviceprovider
                        return await scope.GetService<ITestService>().DemoQuery(context.GetArgument<int>("input"));
                    }
                });

       
    }

您在解析器中创建一个新范围并使用该范围的服务