Convert -- a simple solution to the problem of multi-condition combination of LINQ

In this article, I use clear examples to solve the multi-condition problem of LINQ and have a clear idea. I also carefully described the problem and hoped to help you.

Recently, I have a project preparation function revision. My brother told me to do everything possible to achieve all kinds of LINQ, so a lot of things should be moved from the storage process .. when I wrote the evaluation function yesterday, I encountered a problem of multi-conditional combination of LINQ. The requirements are as follows:

Criteria for Evaluating multiple types of queries:

1. the query type of the Multi-condition of LINQ:

Rating received _ buyer's rating to me, rating received _ seller's rating to me, rating given _ buyer's rating, rating given _ seller's rating

1. Public EnumOpinionsearchtype
2. {
3. Rating received _ buyer's rating = 0,
4. Ratings received by sellers = 1,
5. Comments provided _ my comments to buyers = 2,
6. Comments given _ my comments to sellers = 3
7. }

2. Evaluate the multi-criteria of LINQ:

All, praise, medium rating, negative rating

1. Public EnumOpiniontype
2. {
3. All = 0,
4. Praise = 1,
5. Medium rating = 2,
6. Negative rating = 3
7. }

3. Time for evaluating and querying the multi-condition of LINQ:

All, within a week, within a month, within six months, six months away

1. Public EnumOpiniontime
2. {
3. All = 0,
4. = 1 in a week,
5. Less than one month = 2,
6. Less than six months = 3,
7. 6 months away = 4
8. }

For caching purposes, you need to upload the expression to the interface to obtain the corresponding list <comment>,

There are 3 conditions in total and 13 sub-conditions. After the combination is arranged, there will be 80 combinations.-If you really write them one by one, it's really tiring ..

The best way is to split all three conditions, complete different expressions, and combine the three conditions to form a new expression. the comparison found on the Internet is only the single-condition parameter. After checking msdn, we can see that there is an expression. and (left, right) can fulfill my needs. exploitation. the Extension Method of net3.5 is written as a combination expression method, and several multi-parameter expressions are reloaded, as follows:

1. # Region expression
2. Public StaticExpression contactexpressions (ThisExpression exp,ParamsExpression [] exps ){
3. Foreach(VAR EInExps ){
4. If(Null= E)Continue;
5. Exp = expression. And (exp, e );
6. }
7. ReturnExp;
8. }
9. Public StaticExpression <func> contactexpressions (ThisExpression exp,ParamsExpression [] exps ){
10. Foreach(VAR EInExps ){
11. If(Null= E)Continue;
12. Exp = expression. And (exp, e );
13. }
14. Return(Expression <func>) exp;
15. }
16.  
17.  Public StaticExpression <func <t1, T> contactexpressions <t1, T> (ThisExpression exp,ParamsExpression [] exps ){
18. Foreach(VAR EInExps ){
19. If(Null= E)Continue;
20. Exp = expression. And (exp, e );
21. }
22. Return(Expression <func <t1, T>) exp;
23. }
24.  Public StaticExpression <func <T1, T2, T> contactexpressions <T1, T2, T> (ThisExpression exp,ParamsExpression [] exps ){
25. Foreach(VAR EInExps ){
26. If(Null= E)Continue;
27. Exp = expression. And (exp, e );
28. }
29. Return(Expression <func <T1, T2, T>) exp;
30. }
32.  Public StaticExpression <func <T1, T2, T3, T> contactexpressions <T1, T2, T3, T> (ThisExpression exp,
33.  ParamsExpression [] exps ){
34. Foreach(VAR EInExps ){
35. If(Null= E)Continue;
36. Exp = expression. And (exp, e );
37. }
38. Return(Expression <func <T1, T2, T3, T>) exp;
39. }
41. # Endregion

With these methods for multi-condition query of LINQ, the original requirements can be solved:

1. Expression <func <split_opinion, <span = "">Bool> Exshortarchtype =Null;
2. Expression <func <split_opinion, <span = "">Bool> Expopiniontype =Null;
3. Expression <func <split_opinion, <span = "">Bool> Expopiniontime =Null;
4. Switch(Searchtype ){
5. CaseOpinionsearchtype. Comments _ my comments to buyers:
6. Exshortarchtype = y => Y. userid = userid &&! Y. isseller;
7. Break;
8. CaseOpinionsearchtype. Comments _ my comments to sellers:
9. Exshortarchtype = y => Y. userid = userid & Y. isseller;
10. Break;
11. CaseOpinionsearchtype. Comments received _ Comments from buyers:
12. Exshortarchtype = y => Y. touserid = userid &&! Y. isseller;
13. Break;
14. CaseOpinionsearchtype. Comments received _ Comments the seller gave me:
15. Exshortarchtype = y => Y. touserid = userid &&! Y. isseller;
16. Break;
17. }
18.  Switch(Opintype ){
19. CaseOpiniontype. Praise:
20. Expopiniontype = y => Y. opiniontype = 0;
21. Break;
22. CaseOpiniontype. medium rating:
23. Expopiniontype = y => Y. opiniontype = 1;
24. Break;
25. CaseOpiniontype. Negative rating:
26. Expopiniontype = y => Y. opiniontype = 2;
27. Break;
28. }
29.  Switch(Opintime ){
30. CaseOpiniontime. Within a week:
31. Expopiniontime = y => (datetime. Now-y. opiniontime). Days <= 7;
32. Break;
33. CaseOpiniontime. Within one month:
34. Expopiniontime = y => (datetime. Now-y. opiniontime). Days <= 30;
35. Break;
36. CaseOpiniontime. Within six months:
37. Expopiniontime = y => (datetime. Now-y. opiniontime). Days <= 180;
38. Break;
39. CaseOpiniontime. Six months later:
40. Expopiniontime = y => (datetime. Now-y. opiniontime). days> 180;
41. Break;
42. }
43. // Getpaged (Params) is used to obtain the list and support cache saving.
44.  ReturnGetpaged (exshortarchtype. contactexpressions <split_opinion, <span = "">Bool> (Expopiniontype, expopiniontime ),
45. Userid. usertableprefx (),True, Pageindex, pagesize );

The above describes how to parse the alternative usage of LINQ through a LINQ instance and then solve the problem of multi-condition combination of LINQ.

Address: http://developer.51cto.com/art/200909/151931.htm

Convert -- a simple solution to the problem of multi-condition combination of LINQ