Queryable.SelectMany 方法

参考

定义

命名空间:: System.Linq

程序集:: System.Linq.Queryable.dll

程序集:: System.Core.dll

程序集:: netstandard.dll

重要

一些信息与预发行产品相关，相应产品在发行之前可能会进行重大修改。对于此处提供的信息，Microsoft 不作任何明示或暗示的担保。

将序列的每个元素投影到一个 IEnumerable<T> 并将结果序列组合为一个 IQueryable<T> 类型的序列。

重载

SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource, IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection, TResult>>)	将序列的每个元素投影到一个 IEnumerable<T>，并对其中的每个元素调用结果选择器函数。每个中间序列的结果值都组合为一个一维序列，并将其返回。
SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection, TResult>>)	将序列中的每个元素投影到一个 IEnumerable<T>，它合并了生成它的源元素的索引。对每个中间序列的每个元素调用结果选择器函数，并且将结果值合并为一个一维序列，并将其返回。
SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>)	将序列的每个元素投影到一个 IEnumerable<T>，并将结果序列组合为一个序列。
SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>)	将序列的每个元素投影到一个 IEnumerable<T>，并将结果序列组合为一个序列。每个源元素的索引用于该元素的投影表。

SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource, IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection, TResult>>)

Source:: Queryable.cs

Source:: Queryable.cs

Source:: Queryable.cs

将序列的每个元素投影到一个 IEnumerable<T>，并对其中的每个元素调用结果选择器函数。每个中间序列的结果值都组合为一个一维序列，并将其返回。

public:
generic <typename TSource, typename TCollection, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IQueryable<TResult> ^ SelectMany(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, System::Collections::Generic::IEnumerable<TCollection> ^> ^> ^ collectionSelector, System::Linq::Expressions::Expression<Func<TSource, TCollection, TResult> ^> ^ resultSelector);

public static System.Linq.IQueryable<TResult> SelectMany<TSource,TCollection,TResult> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,System.Collections.Generic.IEnumerable<TCollection>>> collectionSelector, System.Linq.Expressions.Expression<Func<TSource,TCollection,TResult>> resultSelector);

static member SelectMany : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, seq<'Collection>>> * System.Linq.Expressions.Expression<Func<'Source, 'Collection, 'Result>> -> System.Linq.IQueryable<'Result>

<Extension()>
Public Function SelectMany(Of TSource, TCollection, TResult) (source As IQueryable(Of TSource), collectionSelector As Expression(Of Func(Of TSource, IEnumerable(Of TCollection))), resultSelector As Expression(Of Func(Of TSource, TCollection, TResult))) As IQueryable(Of TResult)

类型参数

TSource

source 的元素类型。

TCollection

由 collectionSelector 表示的函数收集的中间元素类型。

TResult

结果序列的元素的类型。

参数

source: IQueryable<TSource>

一个要投影的值序列。

collectionSelector: Expression<Func<TSource,IEnumerable<TCollection>>>

一个应用于输入序列的每个元素的投影函数。

resultSelector: Expression<Func<TSource,TCollection,TResult>>

一个应用于每个中间序列的每个元素的投影函数。

IQueryable<TResult>

一个 IQueryable<T>，其元素是通过对 collectionSelector 的每个元素调用一对多投影函数 source，然后将这些序列元素的每一个及其对应的 source 元素映射到结果元素中的结果。

例外

ArgumentNullException

source、collectionSelector 或 resultSelector 为 null。

示例

下面的代码示例演示如何使用 SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource, IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection, TResult>>) 对数组执行一对多投影。此示例使用结果选择器函数将对应于每个中间序列的源元素保留在对的最后调用 Select的范围内。

class PetOwner
{
    public string Name { get; set; }
    public List<Pet> Pets { get; set; }
}

class Pet
{
    public string Name { get; set; }
    public string Breed { get; set; }
}

public static void SelectManyEx3()
{
    PetOwner[] petOwners =
        { new PetOwner { Name="Higa",
              Pets = new List<Pet>{
                  new Pet { Name="Scruffy", Breed="Poodle" },
                  new Pet { Name="Sam", Breed="Hound" } } },
          new PetOwner { Name="Ashkenazi",
              Pets = new List<Pet>{
                  new Pet { Name="Walker", Breed="Collie" },
                  new Pet { Name="Sugar", Breed="Poodle" } } },
          new PetOwner { Name="Price",
              Pets = new List<Pet>{
                  new Pet { Name="Scratches", Breed="Dachshund" },
                  new Pet { Name="Diesel", Breed="Collie" } } },
          new PetOwner { Name="Hines",
              Pets = new List<Pet>{
                  new Pet { Name="Dusty", Breed="Collie" } } }
        };

    // This query demonstrates how to obtain a sequence of
    // the names of all the pets whose breed is "Collie", while
    // keeping an association with the owner that owns the pet.
    var query =
        petOwners.AsQueryable()
        // Create a sequence of ALL the Pet objects. Then
        // project an anonymous type that consists of each
        // Pet in the new sequence and the PetOwner object
        // from the initial array that corresponds to that pet.
       .SelectMany(owner => owner.Pets,
                   (owner, pet) => new { owner, pet })
        // Filter the sequence of anonymous types to only
        // keep pets whose breed is "Collie".
        .Where(ownerAndPet => ownerAndPet.pet.Breed == "Collie")
        // Project an anonymous type that consists
        // of the pet owner's name and the pet's name.
        .Select(ownerAndPet => new
        {
            Owner = ownerAndPet.owner.Name,
            Pet = ownerAndPet.pet.Name
        });

    // Print the results.
    foreach (var obj in query)
        Console.WriteLine(obj);
}

/* This code produces the following output:

    { Owner = Ashkenazi, Pet = Walker }
    { Owner = Price, Pet = Diesel }
    { Owner = Hines, Pet = Dusty }
*/

Structure PetOwner
    Public Name As String
    Public Pets As List(Of Pet)
End Structure

Structure Pet
    Public Name As String
    Public Breed As String
End Structure

Shared Sub SelectManyEx3()
    Dim petOwners() As PetOwner = _
                {New PetOwner With {.Name = "Higa", _
                      .Pets = New List(Of Pet)(New Pet() { _
                          New Pet With {.Name = "Scruffy", .Breed = "Poodle"}, _
                          New Pet With {.Name = "Sam", .Breed = "Hound"}})}, _
                  New PetOwner With {.Name = "Ashkenazi", _
                      .Pets = New List(Of Pet)(New Pet() { _
                          New Pet With {.Name = "Walker", .Breed = "Collie"}, _
                          New Pet With {.Name = "Sugar", .Breed = "Poodle"}})}, _
                  New PetOwner With {.Name = "Price", _
                      .Pets = New List(Of Pet)(New Pet() { _
                          New Pet With {.Name = "Scratches", .Breed = "Dachshund"}, _
                          New Pet With {.Name = "Diesel", .Breed = "Collie"}})}, _
                  New PetOwner With {.Name = "Hines", _
                      .Pets = New List(Of Pet)(New Pet() { _
                          New Pet With {.Name = "Dusty", .Breed = "Collie"}})} _
                }

    ' This query demonstrates how to obtain a sequence of
    ' the names of all the pets whose breed is "Collie", while
    ' keeping an association with the owner that owns the pet.
    Dim query = petOwners.AsQueryable() _
        .SelectMany(Function(owner) owner.Pets, _
               Function(owner, pet) New With {owner, pet}) _
        .Where(Function(ownerAndPet) ownerAndPet.pet.Breed = "Collie") _
        .Select(Function(ownerAndPet) New With { _
            .Owner = ownerAndPet.owner.Name, _
            .Pet = ownerAndPet.pet.Name})

    Dim output As New System.Text.StringBuilder
    For Each obj In query
        output.AppendLine(String.Format("Owner={0}, Pet={1}", obj.Owner, obj.Pet))
    Next

    ' Display the output.
    MsgBox(output.ToString())
End Sub

' This code produces the following output:

' Owner=Ashkenazi, Pet=Walker
' Owner=Price, Pet=Diesel
' Owner=Hines, Pet=Dusty

注解

此方法至少有一个类型的 Expression<TDelegate> 参数，其类型参数是其中一种 Func<T,TResult> 类型。对于这些参数，可以传入 lambda 表达式，它将编译为 Expression<TDelegate>。

方法 SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource, IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection, TResult>>) 生成一个， MethodCallExpression 表示将调用 SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource, IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection, TResult>>) 自身作为构造的泛型方法。然后，MethodCallExpression CreateQuery(Expression)它将传递给由 Provider 参数的属性表示的的 source 方法IQueryProvider。

由于执行表示调用 SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource, IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection, TResult>>) 的表达式树而发生的查询行为取决于参数类型的 source 实现。预期的行为是，它会调用 collectionSelector 的每个元素 source ，以将其投影到可枚举窗体中。然后，在每个中间序列中的每个元素上调用表示 resultSelector 的函数。生成的值串联成一个一维序列。

适用于

SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection, TResult>>)

Source:: Queryable.cs

Source:: Queryable.cs

Source:: Queryable.cs

将序列中的每个元素投影到一个 IEnumerable<T>，它合并了生成它的源元素的索引。对每个中间序列的每个元素调用结果选择器函数，并且将结果值合并为一个一维序列，并将其返回。

public:
generic <typename TSource, typename TCollection, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IQueryable<TResult> ^ SelectMany(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, int, System::Collections::Generic::IEnumerable<TCollection> ^> ^> ^ collectionSelector, System::Linq::Expressions::Expression<Func<TSource, TCollection, TResult> ^> ^ resultSelector);

public static System.Linq.IQueryable<TResult> SelectMany<TSource,TCollection,TResult> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,int,System.Collections.Generic.IEnumerable<TCollection>>> collectionSelector, System.Linq.Expressions.Expression<Func<TSource,TCollection,TResult>> resultSelector);

static member SelectMany : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, int, seq<'Collection>>> * System.Linq.Expressions.Expression<Func<'Source, 'Collection, 'Result>> -> System.Linq.IQueryable<'Result>

<Extension()>
Public Function SelectMany(Of TSource, TCollection, TResult) (source As IQueryable(Of TSource), collectionSelector As Expression(Of Func(Of TSource, Integer, IEnumerable(Of TCollection))), resultSelector As Expression(Of Func(Of TSource, TCollection, TResult))) As IQueryable(Of TResult)

类型参数

TSource

source 的元素类型。

TCollection

由 collectionSelector 表示的函数收集的中间元素类型。

TResult

结果序列的元素的类型。

参数

source: IQueryable<TSource>

一个要投影的值序列。

collectionSelector: Expression<Func<TSource,Int32,IEnumerable<TCollection>>>

要应用于输入序列的每个元素的投影函数；此函数的第二个参数表示源元素的索引。

resultSelector: Expression<Func<TSource,TCollection,TResult>>

一个应用于每个中间序列的每个元素的投影函数。

IQueryable<TResult>

例外

ArgumentNullException

source、collectionSelector 或 resultSelector 为 null。

注解

方法 SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection, TResult>>) 生成一个， MethodCallExpression 表示将调用 SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection, TResult>>) 自身作为构造的泛型方法。然后，MethodCallExpression CreateQuery(Expression)它将传递给由 Provider 参数的属性表示的的 source 方法IQueryProvider。

由于执行表示调用 SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection, TResult>>) 的表达式树而发生的查询行为取决于参数类型的 source 实现。预期的行为是，它会调用 collectionSelector 的每个元素 source ，以将其投影到可枚举窗体中。每个可枚举结果都包含源元素的索引。然后，在每个中间序列中的每个元素上调用表示 resultSelector 的函数。生成的值串联成一个一维序列。

适用于

SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>)

Source:: Queryable.cs

Source:: Queryable.cs

Source:: Queryable.cs

将序列的每个元素投影到一个 IEnumerable<T>，并将结果序列组合为一个序列。

public:
generic <typename TSource, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IQueryable<TResult> ^ SelectMany(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, System::Collections::Generic::IEnumerable<TResult> ^> ^> ^ selector);

public static System.Linq.IQueryable<TResult> SelectMany<TSource,TResult> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,System.Collections.Generic.IEnumerable<TResult>>> selector);

static member SelectMany : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, seq<'Result>>> -> System.Linq.IQueryable<'Result>

<Extension()>
Public Function SelectMany(Of TSource, TResult) (source As IQueryable(Of TSource), selector As Expression(Of Func(Of TSource, IEnumerable(Of TResult)))) As IQueryable(Of TResult)

类型参数

TSource

source 的元素类型。

TResult

由 selector 表示的函数返回的序列中的元素的类型。

参数

source: IQueryable<TSource>

一个要投影的值序列。

selector: Expression<Func<TSource,IEnumerable<TResult>>>

要应用于每个元素的投影函数。

IQueryable<TResult>

一个 IQueryable<T>，其元素是对输入序列的每个元素调用一对多投影函数的结果。

例外

ArgumentNullException

source 或 selector 为 null。

示例

下面的代码示例演示如何使用 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>) 对数组执行一对多投影。

class PetOwner
{
    public string Name { get; set; }
    public List<String> Pets { get; set; }
}

public static void SelectManyEx1()
{
    PetOwner[] petOwners =
        { new PetOwner { Name="Higa, Sidney",
              Pets = new List<string>{ "Scruffy", "Sam" } },
          new PetOwner { Name="Ashkenazi, Ronen",
              Pets = new List<string>{ "Walker", "Sugar" } },
          new PetOwner { Name="Price, Vernette",
              Pets = new List<string>{ "Scratches", "Diesel" } } };

    // Query using SelectMany().
    IEnumerable<string> query1 =
        petOwners.AsQueryable().SelectMany(petOwner => petOwner.Pets);

    Console.WriteLine("Using SelectMany():");

    // Only one foreach loop is required to iterate through the
    // results because it is a one-dimensional collection.
    foreach (string pet in query1)
        Console.WriteLine(pet);

    // This code shows how to use Select() instead of SelectMany().
    IEnumerable<List<String>> query2 =
        petOwners.AsQueryable().Select(petOwner => petOwner.Pets);

    Console.WriteLine("\nUsing Select():");

    // Notice that two foreach loops are required to iterate through
    // the results because the query returns a collection of arrays.
    foreach (List<String> petList in query2)
    {
        foreach (string pet in petList)
        {
            Console.WriteLine(pet);
        }
        Console.WriteLine();
    }
}

/*
    This code produces the following output:

    Using SelectMany():
    Scruffy
    Sam
    Walker
    Sugar
    Scratches
    Diesel

    Using Select():
    Scruffy
    Sam

    Walker
    Sugar

    Scratches
    Diesel
*/

Structure PetOwner
    Public Name As String
    Public Pets() As String
End Structure

Shared Sub SelectManyEx1()
    Dim petOwners() As PetOwner = _
        {New PetOwner With _
         {.Name = "Higa, Sidney", .Pets = New String() {"Scruffy", "Sam"}}, _
         New PetOwner With _
         {.Name = "Ashkenazi, Ronen", .Pets = New String() {"Walker", "Sugar"}}, _
         New PetOwner With _
         {.Name = "Price, Vernette", .Pets = New String() {"Scratches", "Diesel"}}}

    ' Query using SelectMany().
    Dim query1 As IEnumerable(Of String) = _
                petOwners.AsQueryable().SelectMany(Function(petOwner) petOwner.Pets)

    Dim output As New System.Text.StringBuilder("Using SelectMany():" & vbCrLf)
    ' Only one foreach loop is required to iterate through 
    ' the results because it is a one-dimensional collection.
    For Each pet As String In query1
        output.AppendLine(pet)
    Next

    ' This code shows how to use Select() instead of SelectMany().
    Dim query2 As IEnumerable(Of String()) = _
                petOwners.AsQueryable().Select(Function(petOwner) petOwner.Pets)

    output.AppendLine(vbCrLf & "Using Select():")
    ' Notice that two foreach loops are required to iterate through 
    ' the results because the query returns a collection of arrays.
    For Each petArray() As String In query2
        For Each pet As String In petArray
            output.AppendLine(pet)
        Next
    Next

    ' Display the output.
    MsgBox(output.ToString())
End Sub

' This code produces the following output:

' Using SelectMany():
' Scruffy
' Sam
' Walker
' Sugar
' Scratches
' Diesel

' Using Select():
' Scruffy
' Sam
' Walker
' Sugar
' Scratches
' Diesel

注解

方法 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>) 生成一个， MethodCallExpression 表示将调用 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>) 自身作为构造的泛型方法。然后，MethodCallExpression CreateQuery(Expression)它将传递给由 Provider 参数的属性表示的的 source 方法IQueryProvider。

由于执行表示调用 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>) 的表达式树而发生的查询行为取决于参数类型的 source 实现。预期的行为是，它会调用 selector 的每个元素 source ，以将其投影到可枚举窗体中。然后，它将可枚举结果串联成单个一维序列。

适用于

SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>)

Source:: Queryable.cs

Source:: Queryable.cs

Source:: Queryable.cs

将序列的每个元素投影到一个 IEnumerable<T>，并将结果序列组合为一个序列。每个源元素的索引用于该元素的投影表。

public:
generic <typename TSource, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IQueryable<TResult> ^ SelectMany(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, int, System::Collections::Generic::IEnumerable<TResult> ^> ^> ^ selector);

public static System.Linq.IQueryable<TResult> SelectMany<TSource,TResult> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,int,System.Collections.Generic.IEnumerable<TResult>>> selector);

static member SelectMany : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, int, seq<'Result>>> -> System.Linq.IQueryable<'Result>

<Extension()>
Public Function SelectMany(Of TSource, TResult) (source As IQueryable(Of TSource), selector As Expression(Of Func(Of TSource, Integer, IEnumerable(Of TResult)))) As IQueryable(Of TResult)

类型参数

TSource

source 的元素类型。

TResult

由 selector 表示的函数返回的序列中的元素的类型。

参数

source: IQueryable<TSource>

一个要投影的值序列。

selector: Expression<Func<TSource,Int32,IEnumerable<TResult>>>

要应用于每个元素的投影函数；此函数的第二个参数表示源元素的索引。

IQueryable<TResult>

一个 IQueryable<T>，其元素是对输入序列的每个元素调用一对多投影函数的结果。

例外

ArgumentNullException

source 或 selector 为 null。

示例

下面的代码示例演示如何使用 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>) 对数组执行一对多投影，并使用每个源元素的索引。

class PetOwner
{
    public string Name { get; set; }
    public List<string> Pets { get; set; }
}

public static void SelectManyEx2()
{
    PetOwner[] petOwners =
        { new PetOwner { Name="Higa, Sidney",
              Pets = new List<string>{ "Scruffy", "Sam" } },
          new PetOwner { Name="Ashkenazi, Ronen",
              Pets = new List<string>{ "Walker", "Sugar" } },
          new PetOwner { Name="Price, Vernette",
              Pets = new List<string>{ "Scratches", "Diesel" } },
          new PetOwner { Name="Hines, Patrick",
              Pets = new List<string>{ "Dusty" } } };

    // For each PetOwner element in the source array,
    // project a sequence of strings where each string
    // consists of the index of the PetOwner element in the
    // source array and the name of each pet in PetOwner.Pets.
    IEnumerable<string> query =
        petOwners.AsQueryable()
        .SelectMany(
        (petOwner, index) => petOwner.Pets.Select(pet => index + pet)
        );

    foreach (string pet in query)
        Console.WriteLine(pet);
}

// This code produces the following output:
//
// 0Scruffy
// 0Sam
// 1Walker
// 1Sugar
// 2Scratches
// 2Diesel
// 3Dusty

Structure PetOwner
    Public Name As String
    Public Pets() As String
End Structure

Shared Sub SelectManyEx2()
    Dim petOwners() As PetOwner = _
        {New PetOwner With _
         {.Name = "Higa, Sidney", .Pets = New String() {"Scruffy", "Sam"}}, _
         New PetOwner With _
         {.Name = "Ashkenazi, Ronen", .Pets = New String() {"Walker", "Sugar"}}, _
         New PetOwner With _
         {.Name = "Price, Vernette", .Pets = New String() {"Scratches", "Diesel"}}, _
         New PetOwner With _
         {.Name = "Hines, Patrick", .Pets = New String() {"Dusty"}}}

    ' For each PetOwner element in the source array,
    ' project a sequence of strings where each string
    ' consists of the index of the PetOwner element in the
    ' source array and the name of each pet in PetOwner.Pets.
    Dim query As IEnumerable(Of String) = _
        petOwners.AsQueryable() _
        .SelectMany(Function(petOwner, index) petOwner.Pets.Select(Function(pet) index.ToString() + pet))

    Dim output As New System.Text.StringBuilder
    For Each pet As String In query
        output.AppendLine(pet)
    Next

    ' Display the output.
    MsgBox(output.ToString())
End Sub

' This code produces the following output:
'
' 0Scruffy
' 0Sam
' 1Walker
' 1Sugar
' 2Scratches
' 2Diesel
' 3Dusty

注解

方法 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>) 生成一个， MethodCallExpression 表示将调用 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>) 自身作为构造的泛型方法。然后，MethodCallExpression CreateQuery(Expression)它将传递给由 Provider 参数的属性表示的的 source 方法IQueryProvider。

由于执行表示调用 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>) 的表达式树而发生的查询行为取决于参数类型的 source 实现。预期的行为是，它会调用 selector 的每个元素 source ，以将其投影到可枚举窗体中。每个可枚举结果都包含源元素的索引。然后，它将可枚举结果串联成单个一维序列。

适用于

通过

Queryable.SelectMany 方法

定义

重载

SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource, IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection, TResult>>)

类型参数

参数

返回

例外

示例

注解

适用于

SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection, TResult>>)

类型参数

参数

返回

例外

注解

适用于

SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>)

类型参数

参数

返回

例外

示例

注解

适用于

SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>)

类型参数

参数

返回

例外

示例

注解

适用于

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