整理一下Entity Framework的查询

整理一下Entity Framework的查询

2012-08-30 13:41:59

标签：Entity Framework

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Entity Framework是个好东西，虽然没有Hibernate功能强大，但使用更简便。今天整理一下常见SQL如何用EF来表达，Func形式和Linq形式都会列出来（本人更喜欢Func形式）。

1、简单查询：

SQL：

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

EF：

1. //Func形式

2. var clients = ctx.Clients.Where(c => c.Type == 1 && c.Deleted == 0) 
3. .OrderBy(c => c.ID) 
4. .ToList(); 
6. //Linq形式

7. var clients = from c in ctx.Clients 
8. where c.Type == 1 && c.Deleted==0 
9. orderby c.ID 
10. select c;

2、查询部分字段：

SQL：

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

EF：

1. //Func形式

2. var clients = ctx.Clients.Where(c => c.Status == 1) 
3. .Select(c => new { c.ID, Name = c.ComputerName }) 
4. .ToList(); 
6. //Linq形式

7. var clients = from c in ctx.Clients 
8. where c.Status == 1 
9. select new { c.ID, Name = c.ComputerName }; ：

3、查询单一记录：

SQL：

1. SELECT * FROM [Clients] WHERE ID=100

EF：

1. //Func形式

2. var client = ctx.Clients.FirstOrDefault(c => c.ID == 100); 
4. //Linq形式

5. var client = (from c in ctx.Clients 
6. where c.ID = 100 
7. select c).FirstOrDefault();

4、LEFT JOIN 连接查询

SQL：

1. SELECT c.ID,c.ComputerName,g.Name GroupName  
2. FROM [Clients] c  
3. LEFT JOIN [Groups] g 
4. ON c.GroupID = g.ID 
5. WHERE c.Status=1

EF：

1. //Func形式

2. var clients = ctx.Clients.Where(c => c.Status == 1) 
3. .Select(c => new

4. { 
5. c.ID, 
6. c.ComputerName, 
7. GroupName = ctx.Groups.FirstOrDefault(g => g.ID == c.GroupID).Name 
8. }) 
9. .ToList(); 
11. //Linq形式

12. var clients = from c in ctx.Clients 
13. where c.Status == 1 
14. select new

15. { 
16. c.ID, 
17. c.ComputerName, 
18. GroupName = (from g in ctx.Groups 
19. where g.ID == c.GroupID 
20. select g.Name).FirstOrDefault() 
21. };

5、INNER JOIN 连接查询：

SQL：

1. SELECT c.ID,c.ComputerName,g.Name GroupName  
2. FROM [Clients] c 
3. INNER JOIN [Groups] g 
4. ON c.GroupID = g.ID 
5. WHERE c.Status=1 
6. ORDER BY g.Name

EF：

1. //Func形式

2. var clients = ctx.Clients.Where(c => c.Status == 1) 
3. .Join(ctx.Group, c => c.GroupID, g => g.ID, (c,g) =>  
4. { 
5. c.ID, 
6. c.ComputerName, 
7. GroupName = g.Name 
8. }) 
9. .OrderBy(item => item.GroupName) 
10. .ToList(); 
13. //Linq形式1

14. var clients = from c in ctx.Clients 
15. from g in ctx.Groups 
16. where c.GroupID == g.ID 
17. orderby g.Name 
18. select new

19. { 
20. c.ID, 
21. c.ComputerName, 
22. GroupName = g.Name 
23. }; 
25. //Linq形式2

26. var clients = from c in ctx.Clients 
27. where c.Status == 1 
28. join g in ctx.Group 
29. on c.GroupID equals g.ID into result 
30. from r in result 
31. order by r.Name 
32. select new

33. { 
34. c.ID, 
35. c.ComputerName, 
36. GroupName = r.Name 
37. };

6、分页

SQL：

1. -- 方案1

2. SELECT TOP 10 * FROM [Clients] WHERE Status=1 
3. AND ID NOT IN

4. ( 
5. SELECT TOP 20 ID FROM [Clients] WHERE Status=1 
6. ORDER BY ComputerName 
7. ) 
8. ORDER BY ComputerName 
10. --方案2

11. SELECT * FROM
12. ( 
13. SELECT *, ROW_NUMBER() OVER(ORDER BY ComputerName) AS RowNo 
14. FROM [Clients] 
15. WHERE Status=1 
16. )t 
17. WHERE RowNo >= 20 AND RowNo < 30

EF：

1. //Func形式

2. var clients = ctx.Clients.Where(c => c.Status=1) 
3. .OrderBy(c => c.ComputerName) 
4. .Skip(20) 
5. .Take(10) 
6. .ToList(); 
8. //Linq形式

9. var clients = (from c in ctx.Clients 
10. orderby c.ComputerName 
11. select c).Skip(20).Take(10);

7、分组统计：

SQL：

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

EF：

1. //Func形式

2. var result = ctx.Clients.GroupBy(c => c.Status) 
3. .Select(s => new

4. { 
5. Status = s.Key, 
6. Cnt = s.Count() 
7. }) 
8. .OrderByDescending(r => r.Cnt); 
10. //Linq形式

11. var result = from c in ctx.Clients 
12. group c by c.Status into r 
13. orderby r.Count() descending 
14. select new

15. { 
16. Status = r.Key, 
17. Cnt = r.Count() 
18. };

未完待续……