Atitit. GroupBy LINQ Implementation (1)-----LINQ Framework Selection java. NET PHP

Atitit. GroupBy LINQ Implementation (1)-----LINQ Framework Selection java. net PHP

The implementation method is as follows

1. Dsl/java8 Streams AP, targeted query API, recommended 1

2. Linq::: DSL 1 for like SQL

1.1. linq4j (JDK6 ok,jdk7 compilation error , horse jar download ) 1

1.2. Quaere: LINQon Java ( new sourcecode) 1

1.3. Josql is also API 2 similar to Quaere

1.4.. Net LINQ 2

3. SQL parsing 2

4. Lambda 2

5. GA Self-Implementation 3

1.5. LINQ4J Code 3

6. Apache Collections4 ( no , Trot on groupby) 3

7. Forest Bar ::: self DSL from Stream API jdk8 similar to 3

8. Stream API N LINQ different 3

9. Reference 3

Do report statistics Ah, there is a big problem. There is a whole collection of groupby Query Summary (Sum) No yo?? Already used linq4j,quaere,josql,,Ms to Map The dictionary does not work.

1. Dsl/java8 Streams AP, targeted query API, recommended

Persons1. GroupBy (A = a.name). Select (g = (New {name = G.key, Count

The advantage is that: Type-safe queries, and the ability to use smart tips!

2. Linq::: dsl1.1 of like SQL. LINQ4J (Jdk6 ok,jdk7Compile Error,another horse .JarDownload)

Linq4j d fun0, Fun1, fun2 is not a good DSL either.

Author :: Old Wow's paw attilax ayron,email:[email protected]

Reprint please indicate source: Http://blog.csdn.net/attilax

1.2. Quaere:Javaon theLINQ(not new.sourcecode)

The following example obtains a list of product names from a product list:

List products = Arrays.aslist (Product.getallproducts ());
Iterable Productnames =
From ("P").
Select ("P.getproductname ()");

1.3.JosqlAlso withQuaeresimilar toAPI

This is a jar to download ... doesn't seem to support list (map), only list (bean)

caused by: java.lang.IllegalArgumentException : Cannot find method with Name:url in Class:java.util.Map

1.4.. NET LINQ

Statement Description: LINQ uses Group by and count to get the number of products in each CategoryID.

Description: First by CategoryID classification, remove the CategoryID value and the number of individual products.

1. Counting

1 var q =

2 from P in db. Products

3 Group p by P.categoryid into G

4 Select New {

5 G.key,

6 numproducts = g. Count ()

7};

3. SQL parsing

The disadvantage is that you cannot use the IDE smart hints

4. Lambda

5. GA Self-Realization

1.5. LINQ4J Code

linq4j. asEnumerable (emps)

            . GroupBy (

emp_deptno_selector , new Function0<< /c7>String>() {

public String apply() {

return null;

}

                 } &NBSP; new &NBSP; function2 < string &NBSP; employee &NBSP; string > ()  {

public string Apply (string /c8>v1, Employee e0) {

                    return v1 == NULL ? E0.name : (v1 + "+" + E0.name);

}

                 } &NBSP; new &NBSP; function2 < integer &NBSP; string &NBSP; string > ()  {

                    public   string &NBSP; apply ( integer  , v1 Span style= "COLOR: #707070" >  string   v2 )  {

return v1 + ":" + v2;

}

})

            . by (Functions.<String>identityselector())

            . toList ()

            . toString ();

6. Apache Collections4 (No, trot on GroupBy) 7. Lin Bar::: Own DSL from stream API jdk8 similar to 8. Stream API N LINQ differs

Stream is a lambda -based DSL, syntax not with a SQL Jas 10 ... This is more flexible . ...

Linq, Jas 10 DSL, walk Ten syntax with a SQL Jas 10 . LINQ is easier ...

9. Reference

How to convert a common LINQ expression to a Java 8 Streams API expression.

Linq uses Group by Experience summary -51cto.com.htm

Java8 How to perform stream,reduce,collection operations -51cto.com.htm