ADO.NET Entity Framework学习笔记(5)ESQL查询语句
比起 LINQ to SQL，EF 除了提供 LINQ 查询方式, 还提供了 Entity SQL language
ESQL 类似 Hibernate 的 HSQL，ESQL 与SQL 语言的语法相似，以字符串的方式执行
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esql的查询结果集 ObjectQuery ObjectQuery<实体>myContext context = new myContext();
string esql = "SELECT VALUE DBItemList FROM myContext.DBItemList";
// ObjectQuery<DBItemList> query = new ObjectQuery<DBItemList>(esql, context);
ObjectQuery<DBItemList> query = context.CreateQuery<DBItemList>(esql);
foreach (DBItemList r in query)
{
Console.WriteLine(r.NameID);
}
myContext context = new myContext();
string esql = "SELECT VALUE it FROM myContext.DBItemList as it";
// ObjectQuery<DBItemList> query = new ObjectQuery<DBItemList>(esql, context);
ObjectQuery<DBItemList> query = context.CreateQuery<DBItemList>(esql);
foreach (DBItemList r in query)
{
Console.WriteLine(r.NameID);
}
ObjectQuery<DbDataRecord>myContext context = new myContext();
string esql = "SELECT it.NameID FROM myContext.DBItemList as it";
//ObjectQuery<DbDataRecord> query = new ObjectQuery<DbDataRecord>(esql, context);
ObjectQuery<DbDataRecord> query = context.CreateQuery<DbDataRecord>(esql);
foreach (DbDataRecord r in query)
{
Console.WriteLine(r["NameID"].ToString());
}
ObjectQuery<简单类型>myContext context = new myContext();
string esql = "SELECT value count(it.NameID) FROM myContext.DBItemList as it";
// ObjectQuery<int> query = new ObjectQuery<int>(esql, context);
ObjectQuery<int> query = context.CreateQuery<int>(esql);
foreach (int n in query)
{
Console.WriteLine(n);
}
myContext context = new myContext();
string esql = "SELECT value it.NameID FROM myContext.DBItemList as it";
// ObjectQuery<int> query = new ObjectQuery<int>(esql, context);
ObjectQuery<string> query = context.CreateQuery<string>(esql);
foreach (string n in query)
{
Console.WriteLine(n);
}
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esql的使用可以在
ObjectQuery的Linq方法, 构造ObjectQuery, context.CreateQuery返方法,中使用esql,并得到返回的榄查询结果ObjectQuery
it关键字[it] 出现在 ESQL 中, 由 ObjectQuery<T>.Name 属性设定，用于标示源查询对象(ObjectQuery)的名称，
类似于 "SELECT * FROM Tab as it WHERE it.ItemValue =14" 。
可以将这个默认值 "it" 改成其他字符串。
myContext context = new myContext();
context.DBItemList.Name = "wxd";
ObjectQuery<DBItemList> list = context.DBItemList.Where("wxd.ItemValue=5");
myContext context = new myContext();
var sql = "SELECT VALUE DBItemList FROM myContext.DBItemList";
var query = new ObjectQuery<DBItemList>(sql, context);
query.Name = "wxd";
ObjectQuery<DBItemList> list = query.Where("wxd.ItemValue=@v", new ObjectParameter("v", 5));
value 关键字value 后只能返回一个成员
myContext context = new myContext();
string esql = "SELECT value AVG(it.ItemValue) FROM myContext.DBItemList as it";
ObjectQuery<int> query = context.CreateQuery<int>(esql);
foreach (int n in query)
{
Console.WriteLine(n);
}
/* print:
3
*/
string esql = "select value it.ItemID from myContext.DBItemList as it";
ObjectQuery<string> query = context.CreateQuery<string>(esql);
foreach (string r in query)
{
Console.WriteLine(r);
}
myContext context = new myContext();
string esql = "select value row( it.ItemValue ,it.NameID,'wxd' as wxwinter) from myContext.DBItemList as it";
ObjectQuery<DbDataRecord> query = context.CreateQuery<DbDataRecord>(esql);
foreach (DbDataRecord r in query)
{
Console.WriteLine("{0},{1},{2}", r["ItemValue"], r["NameID"], r["wxwinter"]);
}
查询参数的使用myContext context = new myContext();
string esql = "SELECT VALUE it FROM myContext.DBItemList as it where it.ItemValue=@v1 or it.NameID=@v2";
ObjectParameter v1 = new ObjectParameter("v1", 3);
ObjectParameter v2 = new ObjectParameter("v2", "n01");
ObjectQuery<DBItemList> query = context.CreateQuery<DBItemList>(esql,v1,v2);
foreach (DBItemList r in query)
{
Console.WriteLine("{0},{1}",r.NameID,r.ItemValue);
}
中文字段使用[]将字段括起来
myContext context = new myContext();
ObjectQuery<typeTest> query = context.typeTest.Where("it.值 ==22.22");
System.Console.WriteLine(query.CommandText);
foreach (typeTest r in query)
{
Console.WriteLine("{0},{1},{2},{3},{4},{5}", r.a, r.b, r.c, r.d, r.e, r.值);
}
myContext context = new myContext();
ObjectQuery<typeTest> query = context.typeTest.Where("it.[值] ==22.22");
System.Console.WriteLine(query.CommandText);
foreach (typeTest r in query)
{
Console.WriteLine("{0},{1},{2},{3},{4},{5}", r.a, r.b, r.c, r.d, r.e, r.值);
}
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得到esql与sql字串myContext context = new myContext();
string esql = "SELECT VALUE it FROM myContext.DBItemList as it";
ObjectQuery<DBItemList> query = context.CreateQuery<DBItemList>(esql);
Console.WriteLine(query.CommandText);
Console.WriteLine(query.ToTraceString())
SELECT VALUE it FROM myContext.DBItemList as it
SELECT
[Extent1].[AutoId] AS [AutoId],
[Extent1].[NameID] AS [NameID],
[Extent1].[ItemID] AS [ItemID],
[Extent1].[ItemValue] AS [ItemValue]
FROM [dbo].[DBItemList] AS [Extent1]
CommandText属性得到esql字串
ToTraceString方法得到sql字串
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ObjectQuery的Linq方法 Where用字符串为条件进行查询
ObjectQuery<T> Where(string predicate, params ObjectParameter[] parameters);
myContext context = new myContext();
ObjectQuery<DBItemList> list = context.DBItemList.Where("(it.ItemValue=5 or it .ItemValue=5) and it.NameID='n01'");
SELECT
[Extent1].[AutoId] AS [AutoId],
[Extent1].[NameID] AS [NameID],
[Extent1].[ItemID] AS [ItemID],
[Extent1].[ItemValue] AS [ItemValue]
FROM [dbo].[DBItemList] AS [Extent1]
WHERE (([Extent1].[ItemValue] = 5) OR ([Extent1].[ItemValue] = 5)) AND ([Extent1].[NameID] = 'n01')
OrderBy排序
ObjectQuery<T> OrderBy(string keys, params ObjectParameter[] parameters);
myContext context = new myContext();
ObjectQuery<DBItemList> query = context.DBItemList.OrderBy("it.ItemValue,it.ItemID desc");
foreach (var r in query)
{
Console.WriteLine("{0},{1},{2},{3}", r.AutoId, r.ItemID, r.NameID, r.ItemValue);
}
SELECT
[Extent1].[AutoId] AS [AutoId],
[Extent1].[NameID] AS [NameID],
[Extent1].[ItemID] AS [ItemID],
[Extent1].[ItemValue] AS [ItemValue]
FROM [dbo].[DBItemList] AS [Extent1]
ORDER BY [Extent1].[ItemValue] ASC, [Extent1].[ItemID] DESC
Select射影
ObjectQuery<DbDataRecord> Select(string projection, params ObjectParameter[] parameters);
myContext context = new myContext();
ObjectQuery<DbDataRecord> list = context.DBItemList.Select(" it.ItemValue as a,it.NameID ");
SELECT
1 AS [C1],
[Extent1].[ItemValue] AS [ItemValue],
[Extent1].[NameID] AS [NameID]
FROM [dbo].[DBItemList] AS [Extent1]
SelectValue(projection)返回只有一组字段的数组
ObjectQuery<TResultType> SelectValue<TResultType>(string projection, params ObjectParameter[] parameters);
myContext context = new myContext();
ObjectQuery<int> query = context.DBItemList.SelectValue<int>("it.ItemValue + it.AutoID");
foreach (var r in query)
{
Console.WriteLine(r);
}
SELECT
[Extent1].[ItemValue] + [Extent1].[AutoId] AS [C1]
FROM [dbo].[DBItemList] AS [Extent1]
Top(count)集合的前n个元素
count : 前n个元素
ObjectQuery<T> Top(string count, params ObjectParameter[] parameters);
myContext context = new myContext();
ObjectQuery<DBItemList> query = context.DBItemList.Top("3"); ;
foreach (var r in query)
{
Console.WriteLine("{0},{1},{2},{3}", r.AutoId, r.ItemID, r.NameID, r.ItemValue);
}
SELECT TOP (3)
[c].[AutoId] AS [AutoId],
[c].[NameID] AS [NameID],
[c].[ItemID] AS [ItemID],
[c].[ItemValue] AS [ItemValue]
FROM [dbo].[DBItemList] AS [c]
Skip(keys,count)跳过集合的前n个元素,
keys : 用于排序的字段
count : 要跳过的记录个数
ObjectQuery<T> Skip(string keys, string count, params ObjectParameter[] parameters);
myContext context = new myContext();
ObjectQuery<DBItemList> query = context.DBItemList.Skip("it.ItemValue", "5");
foreach (var r in query)
{
Console.WriteLine("{0},{1},{2},{3}", r.AutoId, r.ItemID, r.NameID, r.ItemValue);
}
SELECT
[Extent1].[AutoId] AS [AutoId],
[Extent1].[NameID] AS [NameID],
[Extent1].[ItemID] AS [ItemID],
[Extent1].[ItemValue] AS [ItemValue]
FROM ( SELECT [Extent1].[AutoId] AS [AutoId], [Extent1].[NameID] AS [NameID], [Extent1].[ItemID] AS [ItemID], [Extent1].[ItemValue] AS [ItemValue], row_number() OVER (ORDER BY [Extent1].[ItemValue] ASC) AS [row_number]
????FROM [dbo].[DBItemList] AS [Extent1]
) AS [Extent1]
WHERE [Extent1].[row_number] > 5
ORDER BY [Extent1].[ItemValue] ASC
分页 Skip TopSkip与Top一起使用
myContext context = new myContext();
ObjectQuery<DBItemList> query = context.DBItemList.Skip("it.ItemValue", "5").Top("3"); ;
foreach (var r in query)
{
Console.WriteLine("{0},{1},{2},{3}", r.AutoId, r.ItemID, r.NameID, r.ItemValue);
}
SELECT TOP (3)
[Extent1].[AutoId] AS [AutoId],
[Extent1].[NameID] AS [NameID],
[Extent1].[ItemID] AS [ItemID],
[Extent1].[ItemValue] AS [ItemValue]
FROM ( SELECT [Extent1].[AutoId] AS [AutoId], [Extent1].[NameID] AS [NameID], [Extent1].[ItemID] AS [ItemID], [Extent1].[ItemValue] AS [ItemValue], row_number() OVER (ORDER BY [Extent1].[ItemValue] ASC) AS [row_number]
????FROM [dbo].[DBItemList] AS [Extent1]
) AS [Extent1]
WHERE [Extent1].[row_number] > 5
ORDER BY [Extent1].[ItemValue] ASC
GroupBy(keys,projection)分组
keys: GROUP BY的字段
projection : Select 的内容
ObjectQuery<DbDataRecord> GroupBy(string keys, string projection, params ObjectParameter[] parameters);
myContext context = new myContext();
ObjectQuery<DbDataRecord> query = context.DBItemList.GroupBy("it.ItemID", "it.ItemID,Sum(it.ItemValue) as ValueSum");
foreach (var r in query)
{
Console.WriteLine("{0},{1}", r["ItemID"], r["ValueSum"]);
}
/*
a,23
b,8
c,23
*/
SELECT
1 AS [C1],
[GroupBy1].[K1] AS [ItemID],
[GroupBy1].[A1] AS [C2]
FROM ( SELECT
????[Extent1].[ItemID] AS [K1],
????SUM([Extent1].[ItemValue]) AS [A1]
????FROM [dbo].[DBItemList] AS [Extent1]
????GROUP BY [Extent1].[ItemID]
) AS [GroupBy1]
SELECT it.ItemID,Sum(it.ItemValue) as ValueSum
FROM ( [DBItemList] ) AS it
GROUP BY it.ItemID
Include(path)加载关联数据,参数为实体的[导航属性]的字串,调用Include("导航属性")后,关联数据会加载,这样就不用在[实体.导航属性]上调用Load()方法
ObjectQuery<T> Include(string path);
myContext context = new myContext();
var r = context.DBItem.Include("DBItemList");
foreach (var dbitem in r)
{
foreach (var dbitemlist in dbitem.DBItemList)
{
Console.WriteLine("{0},{1}", dbitemlist.NameID, dbitemlist.ItemValue);
}
}
效果与下例相同
myContext context = new myContext();
var r = context.DBItem;
foreach (var dbitem in r)
{
dbitem.DBItemList.Load();
foreach (var dbitemlist in dbitem.DBItemList)
{
Console.WriteLine("{0},{1}", dbitemlist.NameID, dbitemlist.ItemValue);
}
}
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esql注释,成员访问,分行注释
--
成员访问
.
分行
;
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esql运算符 算术运算符加
+
减
-
乘
*
除
/
模
%
负
-
比效运算符等于
=
大于
>
大于等于
>=
空判断
IS NOT NULL
IS NULL
小于
<
小天等于
<=
不等于
border-bottom: 0.5pt solid; padding-left: 7px; pa