EntityFrameWork使用

1、简单查询：

SQL：

1	`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：

1	`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:

1	`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()

};

// INNER JOIN ****************************************************************************
var TelefoneInnerJoinPessoa = Db.Telefones
.AsNoTracking()
.Join(Db.Pessoas, t => t.PessoaId, p => p.PessoaId, (t, p) => new { t, p })
.Select(s => new
{
s.t.PessoaId,
s.p.Nome,
s.t.TelefoneId,
s.t.Ddd,
s.t.Numero
}).AsQueryable();
var TGeracao = TelefoneInnerJoinPessoa.ToList();
// INNER JOIN ****************************************************************************

// LEFT JOIN ****************************************************************************
var PessoaLeftJoinTelefone = Db.Pessoas
.AsNoTracking()
.GroupJoin(Db.Telefones, p => p.PessoaId, t => t.PessoaId, (p, t) => new { p, t })
.SelectMany(temp => temp.t.DefaultIfEmpty(), (p, t) => new
{
t.PessoaId,
p.p.Nome,
TelefoneId = (int?)t.TelefoneId,
t.Ddd,
t.Numero
}).AsQueryable();
var TGeracaoLeft = PessoaLeftJoinTelefone.ToList();
// LEFT JOIN ****************************************************************************

// GROUP BY *****************************************************************************
var TelefonesCountByPessoa =
Db.Telefones.AsNoTracking()
.GroupBy(x => x.PessoaId)
.Select(x => new
{
PessoaId = x.Key,
Quantidade = (int?)x.Count()
})
.Join(Db.Pessoas, a => a.PessoaId, p => p.PessoaId, (a, p) => new { a, p })
.Select(s => new
{
s.a.PessoaId,
s.p.Nome,
Quantidade = s.a.Quantidade ?? 0
}).AsQueryable();
var TGeracaoGroup1 = TelefonesCountByPessoa.ToList();

var TelefonesCountByPessoa1 =
Db.Telefones.AsNoTracking()
.GroupBy(x => x.PessoaId)
.Select(x => new
{
PessoaId = x.Key,
Quantidade = (int?)x.Count()
}).AsQueryable();

var PessoasToTelefonesCountByPessoa1 = Db.Pessoas
.AsNoTracking()
.GroupJoin(TelefonesCountByPessoa1, p => p.PessoaId, a => a.PessoaId, (p, a) => new { p, a })
.SelectMany(temp => temp.a.DefaultIfEmpty(),
(p, a) => new
{
p.p.PessoaId,
Quantidade = a.Quantidade ?? 0,
p.p.Nome
}).AsQueryable();
var TGeracaoGroup2 = PessoasToTelefonesCountByPessoa1.ToList();

var PessoasToTelefonesCountByPessoa3 = Db.Pessoas.Select(x => new
{
x.PessoaId,
x.Nome,
Quantidade = x.Telefones.LongCount()
}).AsQueryable();
var TGeracao3 = PessoasToTelefonesCountByPessoa3.ToList();
// GROUP BY *****************************************************************************

// UNION ALL ****************************************************************************
var TbAUnionAllTbB = Db.TbAs.Select(x => new
{
x.Id,
x.Descricao
}).Concat(Db.TbBs.Select(s => new
{
s.Id,
s.Descricao
})).AsQueryable();

var GeracaoUnionAll = TbAUnionAllTbB.ToList();
// UNION ALL ****************************************************************************

//IN, NOT IN, EXISTS e NOT EXISTS
//IN
ICollection<int> Lista = Db.TbBs
.AsNoTracking()
.Select(x => x.Id).ToList<int>();
ICollection<int> lista = new List<int>() { 1, 2 }; VALORES FIXOS

var SelectIn = Db.TbAs
.AsNoTracking()
.Where(x => Lista.Contains(x.Id))
.AsQueryable();

var GeracaoTIn = SelectIn.ToList();

//NOT IN
var SelectNotIn = Db.TbAs
.AsNoTracking()
.Where(x => !Lista.Contains(x.Id))
.AsQueryable();
var GeracaoTNotIn = SelectNotIn.ToList();
//IN, NOT IN, EXISTS e NOT EXISTS

EXISTS
var SelectExists = Db.TbAs
.AsNoTracking()
.Where(x => Db.TbBs.Select(a => a.Id).Contains(x.Id))
.AsQueryable();

var GeracaoTExists = SelectExists.ToList();

EXISTS
var SelectNotExists = Db.TbAs
.AsNoTracking()
.Where(x => !Db.TbBs.Select(a => a.Id).Contains(x.Id))
.AsQueryable();

var GeracaoTNotExists = SelectNotExists.ToList();

T-SQL的IN：

Select ProductID, ProductName, CategoryID
From dbo.Products
Where CategoryID in (1, 2)

T-SQL的NOT IN：

Select ProductID, ProductName, CategoryID
From dbo.Products
Where CategoryID not in (1, 2)

Select ProductID, ProductName, CategoryID
From dbo.Products
Where not CategoryID in (1, 2)

LINQ的IN：

var queryResult = from p in db.Products
where (new int?[] {1,2}).Contains(p.CategoryID)
select p;

LINQ的IN解析成SQL：

SELECT [t0].[ProductID], [t0].[ProductName], [t0].[SupplierID], [t0].[CategoryID], [t0].[QuantityPerUnit], [t0].[UnitPrice], [t0].[UnitsInStock], [t0].[UnitsOnOrder], [t0].[ReorderLevel], [t0].[Discontinued]
FROM [dbo].[Products]AS [t0]
WHERE [t0].[CategoryID] IN (@p0, @p1)

LINQ的NOT IN：

var queryResult = from p in db.Products
where ! (new int?[] {1,2}).Contains(p.CategoryID)
select p;

LINQ的NOT IN解析成SQL：

Entity FrameWork 取表中字段的最大值

int? max = (from t in context.Test

                        select (int?)t.ID).Max();

            int m = 0;

            if (!max.HasValue)

            {

                m = 1;

            }

            else

                m = (int)max + 1;

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EntityFrameWork使用

Entity FrameWork 取表中字段的最大值

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