一直在玩ef核心，并且在include语句中遇到了问题。对于这个代码我得到2家公司，这是我所期望的。
public IEnumerable<Company> GetAllCompanies(HsDbContext db)
{
var c = db.Company;
return c;
}
这回来了
[{"id":1,"companyName":"new","admins":null,"employees":null,"courses":null},
{"id":2,"companyName":"Test Company","admins":null,"employees":null,"courses":null}]
正如你所看到的，有两家公司，所有相关的属性都是null，因为我曾经使用任何包含，这是我所期望的。现在当我将方法更新为：
public IEnumerable<Company> GetAllCompanies(HsDbContext db)
{
var c = db.Company
.Include(t => t.Employees)
.Include(t => t.Admins)
.ToList();
return c;
}
这就是它的回报：
[{"id":1,"companyName":"new",
"admins":[{"id":2,"forename":"User","surname":"1","companyId":1}]
}]
它只返回一家公司，只包括管理员。为什么不包括2家公司及其员工？
public class Company
{
public int Id { get; set; }
public string CompanyName { get; set; }
public List<Admin> Admins { get; set; }
public List<Employee> Employees { get; set; }
public List<Course> Courses { get; set; }
public string GetFullName()
{
return CompanyName;
}
}
public class Employee
{
public int Id { get; set; }
public string Forename { get; set; }
public string Surname { get; set; }
public int CompanyId { get; set; }
[ForeignKey("CompanyId")]
public Company company { get; set; }
public ICollection<EmployeeCourse> Employeecourses { get; set; }
}
public class Admin
{
public int Id { get; set; }
public string Forename { get; set; }
public string Surname { get; set; }
public int CompanyId { get; set; }
[ForeignKey("CompanyId")]
public Company Company { get; set; }
}
我不确定你是否已经看到了接受的答案 题，但问题是JSON Serializer如何处理循环引用。有关更多参考资料的详细信息和链接可以在上面的链接中找到，我建议深入研究这些内容，但简而言之，添加以下内容 startup.cs 将配置序列化程序忽略循环引用：
services.AddMvc()
.AddJsonOptions(options => {
options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
});
我测试你的代码，我的测试中存在这个问题。在这篇文章中 链接 建议使用数据投影。对于你的问题如下所示，是工作。
[HttpGet]
public dynamic Get()
{
var dbContext = new ApplicationContext();
var result = dbContext.Companies
.Select(e => new { e.CompanyName, e.Id, e.Employees, e.Admins })
.ToList();
return result;
}
EF Core无法进行延迟加载。 请参考这里。
或者，您可以使用预先加载。
读这个 文章
下面是我为实现预先加载而创建的扩展方法。
扩展方法：
public static IQueryable<TEntity> IncludeMultiple<TEntity, TProperty>(
this IQueryable<TEntity> source,
List<Expression<Func<TEntity, TProperty>>> navigationPropertyPath) where TEntity : class
{
foreach (var navExpression in navigationPropertyPath)
{
source= source.Include(navExpression);
}
return source.AsQueryable();
}
存储库调用：
public async Task<TEntity> FindOne(ISpecification<TEntity> spec)
{
return await Task.Run(() => Context.Set<TEntity>().AsQueryable().IncludeMultiple(spec.IncludeExpression()).Where(spec.IsSatisfiedBy).FirstOrDefault());
}
用法：
List<object> nestedObjects = new List<object> {new Rules()};
ISpecification<Blog> blogSpec = new BlogSpec(blogId, nestedObjects);
var challenge = await this._blogRepository.FindOne(blogSpec);
依赖关系：
public class BlogSpec : SpecificationBase<Blog>
{
readonly int _blogId;
private readonly List<object> _nestedObjects;
public ChallengeSpec(int blogid, List<object> nestedObjects)
{
this._blogId = blogid;
_nestedObjects = nestedObjects;
}
public override Expression<Func<Challenge, bool>> SpecExpression
{
get { return blogSpec => blogSpec.Id == this._blogId; }
}
public override List<Expression<Func<Blog, object>>> IncludeExpression()
{
List<Expression<Func<Blog, object>>> tobeIncluded = new List<Expression<Func<Blog, object>>>();
if (_nestedObjects != null)
foreach (var nestedObject in _nestedObjects)
{
if (nestedObject is Rules)
{
Expression<Func<Blog, object>> expr = blog => blog.Rules;
tobeIncluded.Add(expr);
}
}
return tobeIncluded;
}
如果它有帮助会很高兴。请注意，这不是生产就绪代码。