EntityFrameWork使用

1、简单查询：

SQL：

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

EF：

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//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：

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

EF：

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//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:

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1	SELECT * FROM [Clients] WHERE ID=100

EF：

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//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：

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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：

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//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：

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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：

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//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：

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-- 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：

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//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：

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SELECT  Status ,         COUNT(*) AS Cnt FROM    [Clients] GROUP BY Status ORDER BY COUNT(*) DESC

EF：

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//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)

Or

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：

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 NOT [t0].[CategoryID] IN (@p0, @p1)

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;