2024最新版python中j-pythonj基础笔记

# Linq.J A Memory-based Object Query language [中文](./README-zh.md) / English `Java uses Linq capabilities similar to C#` [C# Linq](https://learn.microsoft.com/zh-cn/dotnet/csharp/linq/) <p> <a href="https://www.erupt.xyz" target="_blank"><img src="https://img.shields.io/badge/Linq.J-brightgreen" alt="Erupt Framework"></a> <a href="https://mvnrepository.com/search?q=linq.j"><img src="https://img.shields.io/maven-central/v/xyz.erupt/linq.j" alt="maven-central"></a> <a href="https://www.oracle.com/technetwork/java/javase/downloads/index.html"><img src="https://img.shields.io/badge/JDK-8+-green.svg" alt="jdk 8+"></a> <a href="./LICENSE"><img src="https://img.shields.io/badge/license-MIT-blue" alt="license Apache 2.0"></a> <a href='https://gitee.com/erupt/linq/stargazers'><img src='https://gitee.com/erupt/linq/badge/star.svg?theme=gray' alt='GitEE star' ></img></a> <a href="https://github.com/erupts/linq.j"><img src="https://img.shields.io/github/stars/erupts/linq.j?style=social" alt="GitHub stars"></a> </p> ### Linq is Object oriented sql, linq is actually a query on the data in memory, enabling developers to write queries more easily. These query expressions look a lot like SQL > You can join, filter, sort, and group data sources with minimal code. These operations can be combined in a single query to obtain more complex results #### allows you to write Java code that manipulates in-memory data in the same way that you query a database, for example - List, Array - SQL result data - CSV, XML, JSON document datasets - Stream, File stream #### Application Scenarios - Result association for RPCS such as Feign/Dubbo during distributed development - In-memory computation of heterogeneous system data - Use code to organize SQL result data - Sorted aggregation of multiple result objects with in-memory paging - Semantic object transformation and mapping - Clean code, no need for loops and branches to manipulate data - Federated access across data sources #### Operation syntax `From` `Select` `Distinct`、`Join`、`Where`、`Group By`、`Order By`、`Limit`、`Offset`、`...` #### Tips ⚠️ Note: The object field must have a get method to facilitate lambda lookup. It is recommended to use the **Lombok** @Getter annotation to quickly create get access to the field #### How to Use It has zero external dependencies and is only 50kb in size ```xml <dependency> <groupId>xyz.erupt</groupId> <artifactId>linq.j</artifactId> <version>0.0.5</version> </dependency> ``` #### Example 1 ```javascript var strings = Linq.from("C", "A", "B", "B").gt(Th::is, "A").orderByDesc(Th::is).write(String.class); // [C, B, B] var integers = Linq.from(1, 2, 3, 7, 6, 5).orderBy(Th::is).write(Integer.class); // [1, 2, 3, 5, 6, 7] var name = Linq.from(data) // left join .innerJoin(target, Target::getId, Data::getId) // where like .like(Data::getName, "a") // select name .select(Data::getName) // distinct .distinct() // order by .orderBy(Data::getName) .write(String.class); ``` #### Example 2 ```java public class ObjectQuery{ private final List<TestSource> source = http.get("https://gw.alipayobjects.com/os/antfincdn/v6MvZBUBsQ/column-data.json"); private final List<TestSourceExt> target = mongodb.query("db.target.find()"); /** * select demo */ public void select(){ // select * Linq.from(source).select(TestSource.class); // select a, b, c Linq.from(source) .select(TestSource::getName, TestSource::getDate, TestSource::getTags) .select(TestSource::getTags, "tag2") // alias .select(Columns.ofx(TestSource::getId, id -> id + "xxx")); // value convert // select count(*), sum(id), max(id) Linq.from(source) .select(Columns.count("count")) .select(Columns.sum(TestSource::getId, "sum")) .select(Columns.max(TestSource::getId, "max")); } /** * join demo */ public void join(){ // left join Linq.from(source).leftJoin(target, TestSourceExt::getId, TestSource::getId) .select(TestSource.class) .select(TestSourceExt::getName) .select(TestSourceExt2::getValue); // right join Linq.from(source).rightJoin(target, TestSourceExt::getId, TestSource::getId); // inner join Linq.from(source).innerJoin(target, TestSourceExt::getId, TestSource::getId); // full join Linq.from(source).fullJoin(target, TestSourceExt::getId, TestSource::getId); } /** * where demo */ public void where() { // = Linq.from(source).eq(TestSource::getName, "Thanos").select(Columns.count(countAlias)).writeOne(Integer.class); // >=:lval and <=:rval Linq.from(source).between(TestSource::getId, 1, 3); // in (x,x,x) Linq.from(source).in(TestSource::getId, 1, 2, 3); // like '%x%' Linq.from(source).like(TestSource::getName, "a"); // is null Linq.from(source).isNull(TestSource::getId); // customer single field where Linq.from(source).where(TestSource::getId, id -> id >= 5); // customer condition or multi field Linq.from(source).where(data -> { String name = data.get(TestSource::getName); Integer age = (Integer)data.get(TestSource::getAge); // name = 'xxx' or age > 10 return "xxx".equals(name) || age > 10; }); } /** * group by demo */ public void groupBy(){ Linq.from(source) .groupBy(TestSource::getName) .select( Columns.of(TestSource::getName, "name"), Columns.min(TestSource::getDate, "min"), Columns.avg(TestSource::getId, "avg"), Columns.count("count"), Columns.count(TestSource::getName, "countName"), Columns.countDistinct(TestSource::getName, "countDistinct") ) .having(row -> Integer.parseInt(row.get("avg").toString()) > 2) .orderBy(TestSource::getAge); } /** * result write demo */ public void write(){ // write List<Object> List<TestSource> list = Linq.from(source).orderByAsc(TestSource::getDate).write(TestSource.class); // write Object TestSource obj = Linq.from(source).limit(3).writeOne(TestSource.class); // write List<Map> List<Map<String, Object>> map = Linq.from(source).writeMap(); // write Map Map<String, Object> mapOne = Linq.from(source).writeMapOne(); } } ``` #### Next iteration plan - [ ] Supports combining multiple query result sets: UNION ALL, UNION, INTERSECT, EXCEPT, UNION BY NAME - [ ] Supports window functions - [ ] Support Nested loop join - [x] supports having - [x] Support group column format group by date(created_at)