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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 Entity Framework(4)ObjectQuery

访问方式

ADO.NET Entity 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 Entity 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 Entity 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 Entity 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();

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原文地址：https://www.cnblogs.com/BuBu/p/2646541.html