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EntityFramework

2024-07-14 00:32:28   230人阅读

1、简单查询：

SQL：

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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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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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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()
                };


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