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https://issues.apache.org/jira/browse/GROOVY-9159?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Paul King closed GROOVY-9159.
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> [GEP] Support LINQ, aka GINQ
> ----------------------------
>
> Key: GROOVY-9159
> URL: https://issues.apache.org/jira/browse/GROOVY-9159
> Project: Groovy
> Issue Type: New Feature
> Reporter: Daniel Sun
> Assignee: Daniel Sun
> Priority: Major
> Labels: features
> Fix For: 4.0.0-beta-1
>
>
> h2. *Ⅰ. Background*
> In order to make querying different types of data sources convenient, we need
> a unified querying interface, i.e. GINQ
> h2. *Ⅱ. Solution*
> h3. *Basic rationale*
> *Groovy User* ==_writes GINQ code_==> *Parrot Parser* ==generates AST==>
> *GINQ Transformation* ==_transforms AST to {{Queryable}} method
> invocations_==> *Bytecode Writer*
> h3. *transforms AST to {{Queryable}} method invocations will be designed for
> different cases*
> # target objects are all collections
> {{Queryable}} method invocations are implemented by Java 8+ stream method
> invocations
> # target objects are all DB related objects
> {{Queryable}} method invocations are implemented by *JOOQ* method
> invocations( [https://github.com/jOOQ/jOOQ] ) as a {{GINQ provider}} in a
> seperate sub-project(e.g. {{groovy-linq-jooq}}). _Note: *JOOQ* is licensed
> under *APL2* too_( [https://github.com/jOOQ/jOOQ/blob/master/LICENSE] )
> # target objects are XML, CSV, etc. related objects, or even mixed types of
> objects
> We can treate the case as a special sub-case of case 1
> h3. *Interfaces & implementations*
> * {{Queryable}}
>
> [https://github.com/danielsun1106/groovy-linq/blob/master/src/main/java/groovy/linq/Queryable.java]
> * {{QueryableCollection}}
>
> [https://github.com/danielsun1106/groovy-linq/blob/master/src/main/java/groovy/linq/QueryableCollection.java]
> h3. *Note:*
> {color:#d04437}1. The exact syntax might be altered before introduction,
> currently working on the general principle.{color}
> 2.GINQ will reuse most of standard SQL syntax, which can make the learning
> curve smooth and avoid infringing the patent of Microsoft.
> 3. All GINQ related keywords are real keywords, e.g. {{from}}, {{where}},
> {{select}}, which is the approach applied by C#. In order to avoid breaking
> existing source code as possible as we can, we should add the new keywords to
> identifiers.
> 4. In order to support type inference better, {{select}} clause is placed at
> the end of GINQ expression.
> 5. {{select P1, P2 ... Pn}} is a simplifed syntax of {{select
> Tuple.tuple(P1, P2 ... Pn)}} and will create a {{List}} of {{Tuple}}
> sub-class instances when and only when {{n >= 2}}
> h2. *Ⅲ. EBNF*
> h3. TBD
> h2. *Ⅳ. Examples*
> h3. 1. Filtering
> {code:java}
> @groovy.transform.EqualsAndHashCode
> class Person {
> String name
> int age
> }
> def persons = [new Person(name: 'Daniel', age: 35), new Person(name: 'Peter',
> age: 10), new Person(name: 'Alice', age: 22)]
> {code}
> h4. 1.1
> {code:java}
> def result =
> from persons p
> where p.age > 15 && p.age <= 35
> select p.name
> assert ['Daniel', 'Alice'] == result
> {code}
> {code:java}
> // interface
> from(persons).where(p -> p.age > 15 && p.age <= 35).select(p ->
> p.name).toList()
> {code}
> {code:java}
> // collection implementation
> persons.stream().filter(p -> p.age > 15 && p.age <= 35).map(p ->
> p.name).collect(Collectors.toList())
> {code}
> h4. 1.2
> {code:java}
> def result =
> from persons p
> where p.age > 15 && p.age <= 35
> select p
> assert [new Person(name: 'Daniel', age: 35), new Person(name: 'Alice', age:
> 22)] == result
> {code}
> {code:java}
> // interface
> from(persons).where(p -> p.age > 15 && p.age <= 35).select(p -> p).toList()
> {code}
> {code:java}
> // collection implementation
> persons.stream().filter(p -> p.age > 15 && p.age <=
> 35).collect(Collectors.toList())
> {code}
> h4. 1.3
> {code:java}
> def numbers = [1, 2, 3]
> def result =
> from numbers t
> where t <= 2
> select t
> assert [1, 2] == result
> {code}
> {code:java}
> // interface
> from(numbers).where(t -> t <= 2).select(t -> t).toList()
> {code}
> {code:java}
> // collection implementation
> numbers.stream().filter(t -> t <= 2).collect(Collectors.toList())
> {code}
> h3. 2. Joining
> {code:java}
> import static groovy.lang.Tuple.*
> @groovy.transform.EqualsAndHashCode
> class Person {
> String name
> int age
> City city
> }
> @groovy.transform.EqualsAndHashCode
> class City {
> String name
> }
> def persons = [new Person(name: 'Daniel', age: 35, city: new City(name:
> 'Shanghai')), new Person(name: 'Peter', age: 10, city: new City(name:
> 'Beijing')), new Person(name: 'Alice', age: 22, city: new City(name:
> 'Hangzhou'))]
> def cities = [new City(name: 'Shanghai'), new City(name: 'Beijing'), new
> City(name: 'Guangzhou')]
> {code}
> h4. 2.1
> {code:java}
> // inner join
> def result =
> from persons p
> innerjoin cities c on p.city.name == c.name
> select p.name, c.name
> assert [tuple('Daniel', 'Shanghai'), tuple('Peter', 'Beijing')] == result
> {code}
> {code:java}
> // interface
> from(persons).innerJoin(from(cities), (p, c) -> p.city.name ==
> c.name).select((p, c) -> tuple(p.name, c.name)).toList()
> {code}
> {code:java}
> // collection implementation
> persons.stream()
> .flatMap(p -> cities.stream().filter(c -> p.city.name == c.name).map(c
> -> tuple(p.name, c.name)))
> .collect(Collectors.toList())
> {code}
> h4. 2.2
> {code:java}
> def result =
> from persons p
> innerjoin cities c on p.city == c
> select p.name
> assert ['Daniel', 'Peter'] == result
> {code}
> {code:java}
> // interface
> from(persons).innerJoin(from(cities), (p, c) -> p.city == c).select((p, c) ->
> p.name).toList()
> {code}
> {code:java}
> // collection implementation
> persons.stream()
> .flatMap(p -> cities.stream().filter(c -> p.city == c).map(c -> p.name))
> .collect(Collectors.toList())
> {code}
> h4. 2.3
> {code:java}
> // left outer join
> def result =
> from persons p
> leftjoin cities c on p.city.name == c.name // same with left outer join
> select p.name, c.name
> assert [tuple('Daniel', 'Shanghai'), tuple('Peter', 'Beijing'),
> tuple('Alice', null)] == result
> {code}
> {code:java}
> // interface
> from(persons).leftjoin(from(cities), (p, c) -> p.city.name ==
> c.name).select((p, c) -> tuple(p.name, c.name)).toList()
> {code}
> {code:java}
> // collection implementation
> persons.stream()
> .flatMap(p ->
> cities.stream()
> .map(c -> p.city.name == c.name ? c : GinqConstant.NULL)
> .reduce(new LinkedList(), (r, e) -> {
> int size = r.size()
> if (0 == size) {
> r.add(e)
> return r
> }
>
> int lastIndex = size - 1
> Object lastElement = r.get(lastIndex)
>
> if (GinqConstant.NULL != e) {
> if (GinqConstant.NULL == lastElement) {
> r.set(lastIndex, e)
> } else {
> r.add(e)
> }
> }
>
> return r
> }).stream()
> .map(c -> Tuple.tuple(p.name, GinqConstant.NULL == c ?
> GinqConstant.NULL : c.name)))
> .collect(Collectors.toList())
> {code}
> h4. 2.4
> {code:java}
> // right outer join
> def result =
> from persons p
> rightjoin cities c on p.city.name == c.name // same with right outer
> join
> select p.name, c.name
> assert [tuple('Daniel', 'Shanghai'), tuple('Peter', 'Beijing'), tuple(null,
> 'Guangzhou')] == result
> {code}
> h3. 3. Projection
> {code:java}
> import static groovy.lang.Tuple.*
> @groovy.transform.EqualsAndHashCode
> class Person {
> String name
> int age
> }
> def persons = [new Person(name: 'Daniel', age: 35), new Person(name: 'Peter',
> age: 10), new Person(name: 'Alice', age: 22)]
> {code}
> h4. 3.1
> {code:java}
> def result =
> from persons p
> select p.name
> assert ['Daniel', 'Peter', 'Alice'] == result
> {code}
> h4. 3.2
> {code:java}
> def result =
> from persons p
> select p.name, p.age
> assert [tuple('Daniel', 35), tuple('Peter', 10), tuple('Alice', 22)] == result
> {code}
> h4. 3.3
> {code:java}
> def result =
> from persons p
> select [name: p.name, age: p.age]
> assert [ [name: 'Daniel', age: 35], [name: 'Peter', age: 10], [name: 'Alice',
> age: 22] ] == result
> {code}
> h4. 3.4
> {code:java}
> def result =
> from persons p
> select new Person(name: p.name, age: p.age)
> assert persons == result
> {code}
> h4. 3.5
> {code:java}
> def result =
> from persons p
> select p
> assert persons == result
> {code}
> h3. 4. Grouping
> {code:java}
> import static groovy.lang.Tuple.*
> @groovy.transform.EqualsAndHashCode
> class Person {
> String name
> int age
> String gender
> }
> def persons = [new Person(name: 'Daniel', age: 35, gender: 'Male'), new
> Person(name: 'Peter', age: 10, gender: 'Male'), new Person(name: 'Alice',
> age: 22, gender: 'Female')]
> {code}
> h4. 4.1
> {code:java}
> def result =
> from persons p
> groupby p.gender
> select p.gender, max(p.age)
> assert [tuple('Male', 35), tuple('Female', 22)] == result
> {code}
> h3. 5. Having
> {code:java}
> import static groovy.lang.Tuple.*
> @groovy.transform.EqualsAndHashCode
> class Person {
> String name
> int age
> String gender
> }
> def persons = [new Person(name: 'Daniel', age: 35, gender: 'Male'), new
> Person(name: 'Peter', age: 10, gender: 'Male'), new Person(name: 'Alice',
> age: 22, gender: 'Female')]
> {code}
> h4. 5.1
> {code:java}
> def result =
> from persons p
> groupby p.gender
> having p.gender == 'Male'
> select p.gender, max(p.age)
> assert [tuple('Male', 35)] == result
> {code}
> h3. 6. Sorting
> {code:java}
> @groovy.transform.EqualsAndHashCode
> class Person {
> String name
> int age
> }
> def persons = [new Person(name: 'Daniel', age: 35), new Person(name: 'Peter',
> age: 10), new Person(name: 'Alice', age: 22)]
> {code}
> h4. 6.1
> {code:java}
> def result =
> from persons p
> orderby p.age
> select p.name
> assert ['Peter', 'Alice', 'Daniel'] == result
> {code}
> h4. 6.2
> {code:java}
> def result =
> from persons p
> orderby p.age desc
> select p.name
> assert ['Daniel', 'Alice', 'Peter'] == result
> {code}
> h3. 7. Pagination
> {code:java}
> def numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
> {code}
> h4. 7.1
> {code:java}
> def result =
> from numbers n
> limit 2, 5
> select n
> assert [2, 3, 4, 5, 6] == result
> {code}
> h4. 7.2
> {code:java}
> def result =
> from numbers n
> limit 5
> select n
> assert [0, 1, 2, 3, 4] == result
> {code}
> h3. 8. Nested Queries
> {code:java}
> def numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
> {code}
> h4. 8.1
> {code:java}
> def result =
> from (
> from numbers n
> where n <= 5
> select n
> ) v
> limit 2, 5
> select v
> assert [2, 3, 4, 5] == result
> {code}
> h3. 9. WITH-Clause
> {code:java}
> def numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
> {code}
> h4. 9.1
> {code:java}
> def result =
> with v as (
> from numbers n
> where n <= 5
> select n
> )
> from v
> limit 2, 5
> select v
> assert [2, 3, 4, 5] == result
> {code}
> h3. 10. Union
> {code:java}
> def numbers1 = [0, 1, 2]
> def numbers2 = [2, 3, 4]
> {code}
> h4. 10.1
> {code:java}
> def result =
> from numbers1 n
> select n
> unionall
> from numbers2 n
> select n
> assert [0, 1, 2, 2, 3, 4] == result
> {code}
> h4. 10.2
> {code:java}
> def result =
> from numbers1 n
> select n
> union
> from numbers2 n
> select n
>
> assert [0, 1, 2, 3, 4] == result
> {code}
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