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https://github.com/sangupta/gather

Run SQL queries on Java objects in a collection
https://github.com/sangupta/gather

dynamic-queries hoc-queries in-memory java java-collections sql sql-query

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Run SQL queries on Java objects in a collection

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README 

        
# Gather



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`Gather` is an ultra-lightweight, 37KB, no dependencies library to fire SQL like queries on Java collections

and arrays. The data is not inserted into any in-memory database, nor any index is created. The query is matched

against all the objects (could be different types as well) against the provided query. Useful to run ad-hoc

queries and aggregation functions, say on XML/JSON/CSV and more.



The library is tested on the following JDK versions:



* Oracle JDK 9

* Oracle JDK 8

* Oracle JDK 7



## Table of Contents



* [Usecases](#usecases)

* [Usage Examples](#usage-examples)

* [Composed Objects and Keys](#composed-objects-and-keys)

* [Features](#features)

* [Roadmap](#roadmap)

* [Clause chaining and Evaluation](#clause-chaining-and-evaluation)

* [Performance](#performance)

* [Downloads](#downloads)

* [Release Notes](#release-notes)

* [Versioning](#versioning)

* [License](#license)



## Usecases



The library is useful in the following scenarios:



* Run ad-hoc queries during development to debug data-sets and tweak DB queries

* Run ad-hoc queries on production data via some admin interface

* Query on objects of different types in one-shot, say `List` than `List`

* Works with JDK 9, 8, 7 and legacy code



## Usage Examples



```java

List employees = this.employeeService.getAllEmployeesFromDatabase();



// prepare a query

Gather query = Gather.where("age").greaterThan(50).and("status").is("active");



// fire query

List filtered = query.find(employees);



// reuse the query for another collection

List managers = this.employeeService.getAllManagersFromDatabase();



List filteredManagers = query.find(managers);



// null check operations

query = Gather.where("name").isNull();

query = Gather.where("name").isNotNull();



// not operator

query = Gather.where("name").not().is("sandeep");



// find instances that have a property

// one of the two ways can be employed

gather = Gather.where("name").existsProperty();

gather = Gather.hasProperty("name");



// query if an attribute which is a collection or an array contains a given value

// converting between various primitive value types is supported

gather = Gather.where("someFloatArray").has(new Double(123));



// run over collections as well

gather = Gather.where("collection").has(objectInstance);



// find a single instance

query.findOne(employees);



// find limited instances

query.find(employees, 5);



// find 5 instances, but skip the first 10 instances

query.find(employees, 5, 10);



// count the number of results rather than accumulating them

// this is much faster and memory efficient

int numResults = query.count(employees);

```



## Composed Objects and Keys



`Gather` supports composed objects and keys in the `where` clause based on them. For example: the

following query will search all objects in the collection/array called `children` which have an `age`

attribute and its value is less than `40`.



```java

Gather query = Gather.where("children.age").lessThan(10);



query.find(employees);



public class Employee {



  public List children;



}



public class Child {



  public int age;



}

```



## Features



* Gathering operations

  * `find` - find all matching objects, with options to skip elements and/or limit number of matches

  * `findOne` - find the first matching object

  * `count` - count the total number of matching objects

  * `aggregate` - run a custom aggregator on a collection/array for a given field

* Supported operations

  * `is` - equals match

  * `isIgnoreCase` - equals match ignoring case on strings

  * `isNull` - check if a property is null

  * `isNotNull` - check if a property is not null

  * `like` - wildcard match on strings

  * `regex` - Java regular expression match on strings

  * `has` - check if value is contained in a collection or an array

  * `hasAll` - check if all values are contained in a collection or an array

  * `hasAny` - check if any of the value are present in a collection or an array

  * `not` - negate the match expression

  * `existsProperty` - check if property exists on object

  * `notExistsProperty` - check if property does not exists on object

  * `lessThan` - if a value is less than property value

  * `lessThanOrEquals` - if a value is equal or less than property value

  * `greaterThan` - if a value is greater than property value

  * `greaterThanOrEquals` - if a value is equal or greater than property value

* Boolean operations supported

  * `and` - Boolean AND between two clauses

  * `or` - Boolean OR between two clauses

* Aggregation operations

  * `averageAsLong` - find average value of a field which has no decimal part

  * `averageAsDouble` - find average value of a field which has a decimal part

  * `minAsLong` - find minimum value of a field which has no decimal part

  * `minAsDouble` - find minimum value of a field which has a decimal part

  * `maxAsLong` - find maximum value of a field which has no decimal part

  * `maxAsDouble` - find maximum value of a field which has a decimal part

  * `sumAsLong` - find total sum of value of a field which has no decimal part

  * `sumAsDouble` - find total sum of value of a field which has a decimal part

  * `unique` - find the number of unique objects from the result set

  * `count` - count objects in a collection/array which have a given field



## RoadMap



* Support for `uniqueAs("someKey", String.class)` to return `Set` than `Set`

* Support for `groupBy("someKey")` to return a `Map>`



## Clause chaining and Evaluation



When more than one clause is added to the query and Boolean operations like `AND` or `OR` are used

to connect them, the evaluation happens from left to right. The first clause is evaluated first and

then the result is boolean `AND`/`OR` with the result of next clause depending on connecting operation

type.



For example:



```java

Gather.where("name").like("sandeep*").and("age").lessThan(50).or("status").is("active");

```



The evaluation happens in the order:



```java

boolean first = evaluate("name like 'sandeep*'");

boolean second = evaluate("age < 50");

boolean third = evaluate("status == 'active'");

return first & second | third;

```



## Performance



Performance numbers and percentage changes (compared to previous run). Values are operations-per-second.

An operation is a query fired over a million objects created randomly for a `LIKE` clause and a `GREATER THAN`

clause.



| Version  |   Date Run   | `LIKE` clause | %age change | Numeric `GREATER THAN` clause | %age change |

|----------|--------------|---------------|-------------|-------------------------------|-------------|

|  1.0.0   | 10 Jan 2018  |     3.240     |     n/a     |        3.215                  |      n/a    |

|  1.2.0   | 10 Jan 2018  |     4.160     |     +28     |        5.792                  |      +80    |

| Snapshot | 10 Jan 2018  |     5.322     |     +28     |        5.735                  |      +0     |



Test Machine specs:



```

Macbook Pro (2017)

2.9GHz Intel i7

16GB RAM

OS X 10.12.6

Oracle JDK 1.8.0_131

Tests run from inside Eclipse Oxygen.2 (4.7.2) release

```



JMH options used were:



```

# JMH version: 1.19

# VM version: JDK 1.8.0_131, VM 25.131-b11

# VM invoker: /Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/bin/java

# VM options: -Dfile.encoding=UTF-8

# Warmup: 5 iterations, 1 s each

# Measurement: 20 iterations, 1 s each

# Timeout: 10 min per iteration

# Forks: 5

# Threads: 1 thread, will synchronize iterations

# Benchmark mode: Throughput, ops/time

```



**Caveat:** Your mileage may vary.



## Downloads



The latest stable release of the library can be downloaded via the Maven Central using the following coordinates:



```xml



  com.sangupta

  gather

  1.2.0



```



The current/latest development snapshot `JAR` can be obtained using `JitPack.io` as:



Add the following repository to Maven,



```xml



  jitpack.io

  https://jitpack.io



```



Then add the dependency as,



```xml



    com.github.sangupta

    gather

    -SNAPSHOT



```



## Release Notes



**Snapshot**



* Improve performance of `wildcard` matches



**1.2.0 (21 Dec 2017)**



* Query on `object arrays` than just `Collections`

* Added caching to improve performance

* Updated for newer OSSRH release guidelines

* Updated `javadocs` and copyright headers



**1.0.0 (09 Jun 2017)**



* First stable release



## Versioning



For transparency and insight into our release cycle, and for striving to maintain

backward compatibility, `gather` will be maintained under the Semantic

Versioning guidelines as much as possible.



Releases will be numbered with the follow format:



```

..

```



And constructed with the following guidelines:



* Breaking backward compatibility bumps the major

* New additions without breaking backward compatibility bumps the minor

* Bug fixes and misc changes bump the patch



For more information on SemVer, please visit http://semver.org/.



## License



```

 gather: SQL queries for Java collections

 Copyright (c) 2017-2018, Sandeep Gupta



 https://sangupta.com/projects/gather



 Licensed under the Apache License, Version 2.0 (the "License");

 you may not use this file except in compliance with the License.

 You may obtain a copy of the License at



      http://www.apache.org/licenses/LICENSE-2.0



 Unless required by applicable law or agreed to in writing, software

 distributed under the License is distributed on an "AS IS" BASIS,

 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 See the License for the specific language governing permissions and

 limitations under the License.

```