[英]Linq parent with multiple children
這些是我的桌子
家長
孩子
學校
我想像這樣拉父母數據
ParentName, ParentEmail, SchoolName, ChildName1, ChildName2
如何在 C# 中使用 Linq 實現這一點?
我試過這個
var result = from parent
join child
join school
但它沒有編譯。
這是一個 linq 查詢,可以滿足您的要求。 我同意 @flydog57 與您的數據結構相關的觀點。 除非您需要強制執行 2 child 規則,否則在 Child 表上有一個 SchoolId 和 Parent1 Parent2 會更有意義,而不是相反。
void Main()
{
var parents = GetParents();
var children = GetChildren();
var schools = GetSchools();
var child1parent = children.Join(parents, c => c.ChildId, p => p.Child1Id, (c, p) => new { Child = c, Parent = p });
var child2parent = children.Join(parents, c => c.ChildId, p => p.Child2Id, (c, p) => new { Child = c, Parent = p });
var results = child1parent
.Join(child2parent, c1 => c1.Parent.Child2Id, c2 => c2.Child.ChildId, (c1, c2) => new { Parent = c1.Parent, Child1 = c1.Child, Child2 = c2.Child })
.Join(schools, x => x.Parent.SchoolId, s => s.SchoolId, (x, s) => new { Parent = x.Parent, Child1 = x.Child1, Child2 = x.Child1, School = s })
.Select(x => new { x.Parent, x.School, x.Child1, x.Child2 });
results.ToList().ForEach(x => Console.WriteLine($"{x.Parent.ParentName} {x.Parent.ParentEmail}, {x.School.SchoolName}, {x.Child1.ChildName}, {x.Child2.ChildName}"));
}
public class Parent
{
public string ParentName { get; set; }
public string ParentEmail { get; set; }
public int Child1Id { get; set; }
public int Child2Id { get; set; }
public int SchoolId { get; set; }
}
public class Child
{
public int ChildId { get; set; }
public string ChildName { get; set; }
}
public class School
{
public int SchoolId { get; set; }
public string SchoolName { get; set; }
}
public List<Parent> GetParents()
{
return
new List<Parent>
{
new Parent { ParentName = "Donald", ParentEmail = "donald@disney.com", Child1Id = 1, Child2Id = 2, SchoolId = 1 },
new Parent { ParentName = "Lulubelle", ParentEmail = "Lulubelle@disney.com", Child1Id = 3, Child2Id = 4, SchoolId = 1 },
};
}
public List<Child> GetChildren()
{
return
new List<Child>
{
new Child { ChildId = 1, ChildName = "Huey" },
new Child { ChildId = 2, ChildName = "Dewey" },
new Child { ChildId = 3, ChildName = "Fethry" },
new Child { ChildId = 4, ChildName = "Abner" }
};
}
public List<School> GetSchools()
{
return
new List<School>
{
new School { SchoolId = 1, SchoolName = "Disney School of Rock" }
};
}
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