EntityFramwork 查询

EntityFramwork 查询

1、简单查询：

SQL：

SELECT * FROM [Clients] WHERE Type=1 AND
Deleted=0 ORDER BY ID

EF：

//Func形式

var clients = ctx.Clients.Where(c =>
c.Type == 1 && c.Deleted == 0)

.OrderBy(c => c.ID)

.ToList();

//Linq形式

var clients = from c in ctx.Clients

where c.Type == 1 &&
c.Deleted==0

orderby c.ID

select c;

2、查询部分字段：

SQL：

SELECT ID,Name FROM [Clients] WHERE
Status=1

EF：

//Func形式

var clients = ctx.Clients.Where(c =>
c.Status == 1)

.Select(c => new { c.ID, Name = c.ComputerName })

.ToList();

//Linq形式

var clients = from c in ctx.Clients

where c.Status == 1

select new { c.ID, Name =
c.ComputerName }; ：

3、查询单一记录：

SQL：

SELECT * FROM [Clients] WHERE ID=100

EF：

//Func形式

var client = ctx.Clients.FirstOrDefault(c
=> c.ID == 100);

//Linq形式

var client = (from c in ctx.Clients

where c.ID = 100

select c).FirstOrDefault();

4、LEFT JOIN 连接查询

SQL：

SELECT c.ID,c.ComputerName,g.Name
GroupName

FROM [Clients] c

LEFT JOIN [Groups] g

ON c.GroupID = g.ID

WHERE c.Status=1

EF：

//Func形式

var clients = ctx.Clients.Where(c =>
c.Status == 1)

.Select(c => new

{

c.ID,

c.ComputerName,

GroupName =
ctx.Groups.FirstOrDefault(g => g.ID == c.GroupID).Name

})

.ToList();

//Linq形式

var clients = from c in ctx.Clients

where c.Status == 1

select new

{

c.ID,

c.ComputerName,

GroupName = (from g in
ctx.Groups

where g.ID ==
c.GroupID

select
g.Name).FirstOrDefault()

};

5、INNER JOIN 连接查询：

SQL：

SELECT c.ID,c.ComputerName,g.Name
GroupName

FROM [Clients] c

INNER JOIN [Groups] g

ON c.GroupID = g.ID

WHERE c.Status=1

ORDER BY g.Name

EF：

//Func形式

var clients = ctx.Clients.Where(c =>
c.Status == 1)

.Join(ctx.Group, c => c.GroupID, g => g.ID, (c,g) =>

{

c.ID,

c.ComputerName,

GroupName = g.Name

})

.OrderBy(item => item.GroupName)

.ToList();

//Linq形式1

var clients = from c in ctx.Clients

from g in ctx.Groups

where c.GroupID == g.ID

orderby g.Name

select new

{

c.ID,

c.ComputerName,

GroupName = g.Name

};

//Linq形式2

var clients = from c in ctx.Clients

where c.Status == 1

join g in ctx.Group

on c.GroupID equals g.ID into result

from r in result

order by r.Name

select new

{

c.ID,

c.ComputerName,

GroupName = r.Name

};

 

6、分页

SQL：

-- 方案1

SELECT TOP 10 * FROM [Clients] WHERE
Status=1

AND ID NOT IN

(

SELECT TOP 20 ID FROM [Clients] WHERE Status=1

ORDER BY ComputerName

)

ORDER BY ComputerName

--方案2

SELECT * FROM

(

SELECT *, ROW_NUMBER() OVER(ORDER BY ComputerName) AS RowNo

FROM [Clients]

WHERE Status=1

)t

WHERE RowNo >= 20 AND RowNo < 30

EF：

//Func形式

var clients = ctx.Clients.Where(c =>
c.Status=1)

.OrderBy(c => c.ComputerName)

.Skip(20)

.Take(10)

.ToList();

//Linq形式

var clients = (from c in ctx.Clients

orderby c.ComputerName

select c).Skip(20).Take(10);

7、分组统计：

SQL：

SELECT Status,COUNT(*) AS Cnt FROM
[Clients]

GROUP BY Status

ORDER BY COUNT(*) DESC

EF：

//Func形式

var result = ctx.Clients.GroupBy(c =>
c.Status)

.Select(s => new

{

Status = s.Key,

Cnt = s.Count()

})

.OrderByDescending(r => r.Cnt);

//Linq形式

var result = from c in ctx.Clients

group c by c.Status into r

orderby r.Count() descending

select new

{

Status = r.Key,

Cnt = r.Count()

};

来自为知笔记(Wiz)