在 ASP.NET Web API 2 上使用 Linq 过滤 IEnumerable 集合

Question

我需要在 ASP.NET Web Api 2 C# 上使用 Linq 根据布尔条件过滤我的数据。但是当我尝试过滤数据时，我的 JSON 数据返回 null。

数据是邀请列表，我想根据 MemberID 和用户是否参加（IsAttending）过滤结果

这是成员模型

public class Member
{
    public int MemberID { get; set; }
    public string MemberName { get; set; }
    public bool IsAdmin { get; set; }
    public bool IsAttending { get; set; }
    public int MemberNumber { get; set; }
    public string PhoneNumber { get; set; }
    public int InviteID { get; set; }
    [JsonIgnore]
    public virtual Invite Iinvite { get; set; }
}

邀请模特

public class Invite
{
    public int InviteID { get; set; }
    public string Subject { get; set; }
    public string DateTime { get; set; }
    public virtual List<Member> Members { get; set; }
}

未经过滤的原始 JSON 数据

[{
    "InviteID": 1,
    "Subject": "Hell",
    "DateTime": "March 2017",
    "Members": [{
        "MemberID": 1,
        "MemberName": "roger",
        "IsAdmin": false,
        "IsAttending": false,
        "MemberNumber": 0,
        "PhoneNumber": null,
        "InviteID": 1
    },
    {
        "MemberID": 2,
        "MemberName": "nkosi",
        "IsAdmin": false,
        "IsAttending": false,
        "MemberNumber": 0,
        "PhoneNumber": null,
        "InviteID": 1
    },
    {
        "MemberID": 3,
        "MemberName": "Mphile",
        "IsAdmin": false,
        "IsAttending": false,
        "MemberNumber": 0,
        "PhoneNumber": null,
        "InviteID": 1
    }]
},
{
    "InviteID": 2,
    "Subject": "Hell",
    "DateTime": "March 2018",
    "Members": [{
        "MemberID": 4,
        "MemberName": "roger",
        "IsAdmin": false,
        "IsAttending": false,
        "MemberNumber": 0,
        "PhoneNumber": null,
        "InviteID": 2
    },
    {
        "MemberID": 5,
        "MemberName": "nkosi",
        "IsAdmin": false,
        "IsAttending": false,
        "MemberNumber": 0,
        "PhoneNumber": null,
        "InviteID": 2
    },
    {
        "MemberID": 6,
        "MemberName": "Mphile",
        "IsAdmin": false,
        "IsAttending": false,
        "MemberNumber": 0,
        "PhoneNumber": null,
        "InviteID": 2
    }]
},
{
    "InviteID": 3,
    "Subject": "Hell",
    "DateTime": "Marchs 2017",
    "Members": [{
        "MemberID": 7,
        "MemberName": "Roger Nkosi",
        "IsAdmin": false,
        "IsAttending": true,
        "MemberNumber": 0,
        "PhoneNumber": null,
        "InviteID": 3
    },
    {
        "MemberID": 8,
        "MemberName": "nkosi",
        "IsAdmin": false,
        "IsAttending": false,
        "MemberNumber": 0,
        "PhoneNumber": null,
        "InviteID": 3
    },
    {
        "MemberID": 9,
        "MemberName": "Mphile",
        "IsAdmin": false,
        "IsAttending": false,
        "MemberNumber": 0,
        "PhoneNumber": null,
        "InviteID": 3
    }]
},
{
    "InviteID": 4,
    "Subject": "Hell",
    "DateTime": "Marchs 2017",
    "Members": [{
        "MemberID": 10,
        "MemberName": "Roger Nkosi",
        "IsAdmin": false,
        "IsAttending": true,
        "MemberNumber": 0,
        "PhoneNumber": null,
        "InviteID": 4
    },
    {
        "MemberID": 11,
        "MemberName": "nkosi",
        "IsAdmin": false,
        "IsAttending": true,
        "MemberNumber": 0,
        "PhoneNumber": null,
        "InviteID": 4
    },
    {
        "MemberID": 12,
        "MemberName": "Mphile",
        "IsAdmin": false,
        "IsAttending": true,
        "MemberNumber": 0,
        "PhoneNumber": null,
        "InviteID": 4
    }]
}]

这是我过滤和返回数据的方式

return db.invites.Include("members").ToList()
                .Where(x => x.Members == db.members
                                .Where(xx => xx.IsAttending == true && xx.MemberID == 4)).ToList();

Answer 1

您想要的并非不可能，只是通过对 DB 的单个 LINQ 查询无法实现。

假设 memberId 包含您要过滤的成员的 id：

var invites = db.invites.Include(i => i.Members).Where(i => i.Members.Any(m => m.IsAttending && m.MemberID == memberId)).ToList(); // db query
invites = invites.Select(i =>
    new Invite
    {
        DateTime = i.DateTime,
        InviteID = i.InviteID,
        Subject = i.Subject,
        Members = i.Members.Where(m => m.IsAttending && m.MemberID == memberId).ToList()
    }).ToList(); // this removes other members (in memory)

 return invites;

Answer 2

您应该使用 Linq Any() 运算符。

它看起来更像

return db.invites.Include("members").Where(x => x.Members.Any(xx => xx.IsAttending && xx.MemberID == 4).ToList()

顺便说一句，我在 db.invites 之后删除了 ToList()，因为这会导致整个成员集合被枚举。不确定您的数据库有多大，但这最终会成为问题。