Question

也许我的眼睛因为我整天都在编码而交叉，但我决定使用linq表达式并且它不会在关键字上编译...请注意这在linqPad中有效。

    using System.Linq;
            public IQueryable<CompanyPerson> PersonsFlattened()
            {

                var contacts = from person in Person
                           join companyPerson in CompanyPerson on person.Id equals companyPerson.PersonId into companyPersonGroups
                           from companyPerson in companyPersonGroups.DefaultIfEmpty()
                           select new
                           {
                               ContactPerson = person,
                               ContactCompany = companyPerson.Company
                           };
}

出于某种原因＆＃34;加入＆＃34;在第2行给我一个错误

＆＃34;无法解析符号＆＃39; GroupJoin＆＃39;＆＃34;

我甚至尝试过另一种方式。

var contacts2 = Person.GroupJoin(CompanyPerson,
                person => person.Id,
                companyPerson => companyPerson.PersonId,
                (person, companyPersonGroups) =>
                    new
                    {
                        person = person,
                        companyPersonGroups = companyPersonGroups
                    }
                ).SelectMany(
                    temp0 => temp0.companyPersonGroups.DefaultIfEmpty(),
                    (temp0, companyPerson) =>
                        new
                        {
                            ContactPerson = temp0.person,
                            ContactCompany = companyPerson.Company
                        }
                );

我得到同样的事情，有什么想法吗？我错过了一些你必须要表达的参考吗？我遍历了对象浏览器，但没有看到我没有包含的任何东西。它是一个web api 2项目.net 4.5

Answer 1

这是因为您提供了类型CompanyPerson而非第一个参数的值：

var contacts2 = Person.GroupJoin(companyPerson,
                person => person.Id,
                companyPerson => companyPerson.PersonId,
                (person, companyPersonGroups) =>
                    new
                    {
                        person = person,
                        companyPersonGroups = companyPersonGroups
                    }
                ).SelectMany(
                    temp0 => temp0.companyPersonGroups.DefaultIfEmpty(),
                    (temp0, companyPerson) =>
                        new
                        {
                            ContactPerson = temp0.person,
                            ContactCompany = companyPerson.Company
                        }
                );

Answer 2

弄清楚GroupJoin编译问题，由于某种原因，它无法使用var contact = xxx正确编译

我必须返回一个QueryAll（Person）

 return _contextProvider.QueryAll<Person>().GroupJoin(...)...

这是最终的解决方案。左sql是否加入并获取人员，即使他们没有与他们相关联的公司。

    [HttpGet]
    public IQueryable<Person> PersonsFlattened()
    {
        //return _contextProvider.QueryAll<Person>();

        var contacts = from person in _contextProvider.QueryAll<Person>()
                       join companyPerson in CompanyPersons() on person.Id equals companyPerson.PersonId into companyPersonGroups
                       from companyPerson in companyPersonGroups.DefaultIfEmpty()
                       select new Person()
                       {
                           FirstName = person.FirstName,
                           LastName = person.LastName

                       };

        return contacts;

    }

Linq“加入”或“GroupJoin”没有编译？ “无法解析符号'GroupJoin'”

2 个答案: