zoukankan      html  css  js  c++  java

  • ADO.NET Entity Framework(4)ObjectQuery

    ObjectQuery<T>数据加载方式

    1. ObjectQuery<T> 提供了一个管理[实体对像]集合

    2. ObjectQuery<T>继承System.Data.Objects.ObjectQuery, ObjectQuery对ObjectContext进行了封装，

    3.可以通过ObjectContext.CreateQuery<T>("esql")的方式创建ObjectQuery<T>

    4.可以通过new ObjectQuery<T>(ObjectContext,"esql")的方式创建ObjectQuery<T>,跟据SQL字串的不同，会得到具体的ObjectQuery<值类型>，或ObjectQuery<DbDataRecord>或ObjectQuery<实体>

    ADO.NET <wbr>Entity <wbr>Framework(4)ObjectQuery

    访问方式

    ADO.NET <wbr>Entity <wbr>Framework(4)ObjectQuery

    Context.CreateQuery<T>()

    string econString = @"

    metadata=res:/myModel.ssdl

    |res:/myModel.csdl

    |res:/myModel.msl

    ;

    provider=System.Data.SqlClient;

    provider connection string=""

    Data Source=.;

    Initial Catalog=LingTestDB;

    Integrated Security=True;

    MultipleActiveResultSets=True;

    ""

    ";

    EntityConnection econ = new EntityConnection(econString);

    ObjectContext context = new ObjectContext(econ);

    ObjectQuery<DBItem> queryTab = context.CreateQuery<DBItem>("select value it from myContext.DBItem as it where it.ItemID='a'");

    foreach (var r in queryTab)

    {

    System.Console.WriteLine("{0},{1}",r.ItemID,r.ItemMatter);

    }

    ObjectQuery<DbDataRecord>

    string econString = @"

    metadata=res:/myModel.ssdl

    |res:/myModel.csdl

    |res:/myModel.msl

    ;

    provider=System.Data.SqlClient;

    provider connection string=""

    Data Source=.;

    Initial Catalog=LingTestDB;

    Integrated Security=True;

    MultipleActiveResultSets=True;

    ""

    ";

    EntityConnection econ = new EntityConnection(econString);

    ObjectContext context = new ObjectContext(econ);

    ObjectQuery<int> queryTab = new ObjectQuery<int>("select value Count(it.ItemID) from myContext.DBItem as it", context);

    foreach (var r in queryTab)

    {

    System.Console.WriteLine("个数:{0}", r.ToString() );

    }

    Execute方法与ObjectResult

    Execute方法

    string econString = @"

    metadata=res:/myModel.ssdl

    |res:/

    SELECT

    [Project2].[ItemID] AS [ItemID],

    [Project2].[C1] AS [C1],

    [Project2].[C2] AS [C2],

    [Project2].[AutoId] AS [AutoId],

    [Project2].[NameID] AS [NameID],

    [Project2].[ItemID1] AS [ItemID1],

    [Project2].[ItemValue] AS [ItemValue]

    FROM ( SELECT

    [Distinct1].[ItemID] AS [ItemID],

    1 AS [C1],

    [Extent2].[AutoId] AS [AutoId],

    [Extent2].[NameID] AS [NameID],

    [Extent2].[ItemID] AS [ItemID1],

    [Extent2].[ItemValue] AS [ItemValue],

    CASE WHEN ([Extent2].[AutoId] IS NULL) THEN CAST(NULL AS int) ELSE1 END AS [C2]

    FROM (SELECT DISTINCT

    [Extent1].[ItemID] AS [ItemID]

    FROM [dbo].[DBItemList] AS [Extent1] ) AS [Distinct1]

    LEFT OUTER JOIN [dbo].[DBItemList] AS [Extent2] ON([Extent2].[ItemID] = [Distinct1].[ItemID]) OR(([Extent2].[ItemID] ISNULL) AND ([Distinct1].[ItemID] IS NULL))

    ) AS [Project2]

    ORDER BY [Project2].[ItemID] ASC, [Project2].[C2] ASC

    ADO.NET <wbr>Entity <wbr>Framework(4)ObjectQuery

    Join

    联合查询

    myContext context1 = new myContext();

    ObjectQuery<DBItem> query1 = context1.DBItem;

    ObjectQuery<DBItemList> query2 = context1.DBItemList;

    var v = query1.Join(query2, temp1 => temp1.ItemID, temp2 => temp2.ItemID, (temp1, temp2) => new{ temp1.ItemID, temp1.ItemMatter, temp2.ItemValue, temp2.AutoId, temp2.NameID });

    foreach (var r in v)

    {

    Console.WriteLine("{0},{1},{2},{3},{4}", r.AutoId, r.ItemID, r.NameID, r.ItemValue,r.ItemMatter);

    }

    myContext context1 = new myContext();

    ObjectQuery<DBItem> query1 = context1.DBItem;

    ObjectQuery<DBItemList> query2 = context1.DBItemList;

    var v = from temp1 in query1 join temp2 in query2 on temp1.ItemID equals temp2.ItemID

    select new { temp1.ItemID, temp1.ItemMatter, temp2.ItemValue, temp2.AutoId,temp2.NameID };

    foreach (var r in v)

    {

    Console.WriteLine("{0},{1},{2},{3},{4}", r.AutoId, r.ItemID, r.NameID, r.ItemValue,r.ItemMatter);

    }

    SELECT

    1 AS [C1],

    [Extent1].[ItemID] AS [ItemID],

    [Extent1].[ItemMatter] AS [ItemMatter],

    [Extent2].[ItemValue] AS [ItemValue],

    [Extent2].[AutoId] AS [AutoId],

    [Extent2].[NameID] AS [NameID]

    FROM [dbo].[DBItem] AS [Extent1]

    INNER JOIN [dbo].[DBItemList] AS [Extent2] ON ([Extent1].[ItemID] =[Extent2].[ItemID]) OR(([Extent1].[ItemID] IS NULL) AND ([Extent2].[ItemID] IS NULL))

    GroupJoin

    myContext context1 = new myContext();

    ObjectQuery<DBItem> query1 = context1.DBItem;

    ObjectQuery<DBItemList> query2 = context1.DBItemList;

    var v = query1.GroupJoin(query2, temp1 => temp1.ItemID, temp2 => temp2.ItemID, (temp1, temp2) =>new { temp1.ItemID, temp1.ItemMatter, 个数 = temp2.Count() });

    foreach (var r in v)

    {

    Console.WriteLine("{0},{1},{2}", r.ItemID, r.ItemMatter,r.个数);

    }

    myContext context1 = new myContext();

    ObjectQuery<DBItem> query1 = context1.DBItem;

    ObjectQuery<DBItemList> query2 = context1.DBItemList;

    var v = from temp1 in query1

    join temp2 in query2 on temp1.ItemID equals temp2.ItemID

    into newtab

    select new { temp1.ItemID, temp1.ItemMatter, 个数 = newtab.Count() };

    foreach (var r in v)

    {

    Console.WriteLine("{0},{1},{2}", r.ItemID, r.ItemMatter,r.个数);

    }

    SELECT

    1 AS [C1],

    [Project1].[ItemID] AS [ItemID],

    [Project1].[ItemMatter] AS [ItemMatter],

    [Project1].[C1] AS [C2]

    FROM ( SELECT

    [Extent1].[ItemID] AS [ItemID],

    [Extent1].[ItemMatter] AS [ItemMatter],

    (SELECT

    COUNT(cast(1 as bit)) AS [A1]

    FROM [dbo].[DBItemList] AS [Extent2]

    WHERE ([Extent1].[ItemID] = [Extent2].[ItemID]) OR (([Extent1].[ItemID] IS NULL) AND ([Extent2].[ItemID]IS NULL))) AS[C1]

    FROM [dbo].[DBItem] AS [Extent1]

    ) AS [Project1]

    ADO.NET <wbr>Entity <wbr>Framework(4)ObjectQuery

    无效的Linq方法

    可将ObjectQuery<T>转换为List<T>后使用 List的对应方法

    Aggregate

    据输入的表达式获取一个聚合值

    myContext context = new myContext();

    List<DBItemList> list = context.DBItemList.ToList();

    DBItemList r = list.Aggregate((x, y) => new DBItemList() { ItemValue = x.ItemValue + y.ItemValue });

    Console.WriteLine("ItemValue合计为:{0}", r.ItemValue);

    //print: ItemValue合计为:54

    TakeWhile

    条件第一次不成立就跳出循环

    myContext context = new myContext();

    List<DBItemList> list = context.DBItemList.ToList();

    IEnumerable<DBItemList> v = list.TakeWhile(p => p.ItemValue >= 2);

    foreach (var r in v)

    {

    Console.WriteLine(r.ItemValue);

    }

    //print

    SkipWhile

    条件第一次不成立就失效，将后面的数据全取

    myContext context = new myContext();

    List<DBItemList> list = context.DBItemList.ToList();

    IEnumerable<DBItemList> v = list.SkipWhile(p => p.ItemValue >= 2);

    foreach (var r in v)

    {

    Console.WriteLine(r.ItemValue);

    }

    //print

    Reverse

    顺序返转

    myContext context = new myContext();

    IEnumerable<DBItemList> list = context.DBItemList.AsEnumerable();

    IEnumerable<DBItemList> v = list.Reverse();

    Last,LastOrDefault

    集合的最后一个元素,集合中没有会报错,

    集合中的最后一个元素,没有则返回类型默认值,对象型默认值为null

    myContext context = new myContext();

    List<DBItemList> list = context.DBItemList.ToList();

    DBItemList l1 = list.Last();

    DBItemList li = list.Last(p=>p.ItemValue==5);

    DBItemList lid = list.LastOrDefault(p => p.ItemValue == 15);

    if (lid != null)

    {

    Console.WriteLine(lid.ItemValue);

    }

    Single,SingleOrDefault

    集合中符合条件的唯一元素,集合中没有会报错,集合中有两个以上会报错

    集合中符合条件的唯一元素,集合中有两个以上会报错,集合中没有则返回类型默认值,对象型默认值为null

    myContext context = new myContext();

    List<DBItemList> list = context.DBItemList.ToList();

    DBItemList di = list.Single(p=>p.ItemValue==5);

    DBItemList did = list.SingleOrDefault(p => p.ItemValue == 15);

    if (did != null)

    {

    Console.WriteLine(did.ItemValue);

    }

    Contains

    判断集合中是否包含有某一元素

    myContext context = new myContext();

    List<DBItemList> list = context.DBItemList.ToList();

    DBItemList r = new DBItemList();

    r.ItemValue = 3;

    bool b = list.Contains(r,new c());

    class c : IEqualityComparer<DBItemList>

    {

    public bool Equals(DBItemList x, DBItemList y)

    {

    if (x.ItemValue == y.ItemValue)

    {

    return true;

    }

    else

    {

    return false;

    }

    }

    public int GetHashCode(DBItemList obj)

    {

    return 0;

    }

    }

    Distinct

    过滤集合中的相同项

    myContext context = new myContext();

    List<DBItemList> list = context.DBItemList.ToList();

    IEnumerable<DBItemList> v = list.Distinct(new c());

    class c : IEqualityComparer<DBItemList>

    {

    public bool Equals(DBItemList x, DBItemList y)

    {

    if (x.ItemValue == y.ItemValue)

    {

    return true;

    }

    else

    {

    return false;

    }

    }

    public int GetHashCode(DBItemList obj)

    {

    return 0;

    }

    }

    ElementAt,ElementAtOrDefault

    集合中指定索引的元素

    集合中指定索引的元素,没有则返回类型默认值,对象型默认值为null

    myContext context = new myContext();

    List<DBItemList> list = context.DBItemList.ToList();

    DBItemList r = list.ElementAt(5);

    DBItemList rd = list.ElementAtOrDefault(50);

    DefaultIfEmpty

    如果集合是的无素为空(count==0),就向集合中插入一个默认元素

    DBItemList r=new DBItemList();

    r.ItemValue=100;

    List<DBItemList> list = new List<DBItemList>();

    var pp = list.DefaultIfEmpty(r);

    SelectMany

    myContext context = new myContext();

    List<DBItemList> query = context.DBItemList.ToList();

    IEnumerable<string> ls=query.SelectMany(p => p.NameID.Split('0'));

    foreach (string r in ls)

    {

    Console.WriteLine(r);

    }

    Lambda表达式

    List<string> ls = new List<string>() { "wxd/1", "lzm/2", "wxwinter/3" };

    var li = ls.SelectMany(p => p.Split('/'));

    foreach (var s in li)

    {

    Console.WriteLine(s);

    }

    ADO.NET <wbr>Entity <wbr>Framework(4)ObjectQuery

    对应Select效果

    var ll = ls.Select(p => p.Split('/'));

    foreach (var s in ll)

    {

    foreach (var ss in s)

    {

    Console.WriteLine(ss);

    }

    }

    SequenceEqual

     

    myContext context = new myContext();

     
  • 相关阅读:
    Entity SQL 初入
    ObjectQuery查询及方法
    Entity Framework 的事务 DbTransaction
    Construct Binary Tree from Preorder and Inorder Traversal
    Reverse Linked List
    Best Time to Buy and Sell Stock
    Remove Duplicates from Sorted Array II
    Reverse Integer
    Implement Stack using Queues
    C++中const限定符的应用
  • 原文地址：https://www.cnblogs.com/BuBu/p/2646541.html
Copyright © 2011-2022 走看看