Lambda2sql (lambda) -> "sql"

Please note: This is a Java 11 library so make sure you have at least Java 13 installed when using it.

Convert Java 8 lambdas to SQL statements.

For example, the following SqlPredicate<Person>:

 person -> person.getAge() < 100 && person.getHeight() > 200

is converted to a string:

  person.age < 100 AND person.height > 200

allowing you to write readable queries in a type safe way.

Usage

int age = 100;
int height = 200;
SqlPredicate<Person> predicate = person -> person.getAge() < age && person.getHeight() > height;

String sql = Lambda2Sql.toSql(predicate); // person.age < 100 AND person.height > 200

How it works

It uses Expressions (based upon JaQue) to build an expression tree for a lambda. The expression tree is then traversed and converted to an SQL WHERE clause.

The following is only for explanatory purposes. You do not need to set this property anywhere, as long as you use the interfaces SqlPredicate<T> and SqlFunction<T>:
Under the hood, JaQue depends on the system property jdk.internal.lambda.dumpProxyClasses, if the lambda expression is not serialized: See https://bugs.openjdk.java.net/browse/JDK-8023524.
When the property is enabled, JVM generated classes for lambdas are saved to disk. JaQue then uses ASM to read the .class files and creates expression trees.

Since the functional interfaces included in this project are automatically serialized, there is no need to set this property. The interfaces SqlPredicate<T> and SqlFunction<T> can be used exactly like the original functional interfaces.

Features

Current version works with predicates, functions and supports the following operators: >, >=, <, <=, =, !=, &&, ||, !. The DateTime API introduced in Java 8 is also supported (.isBefore()/.isAfter()).

It is also possible to achieve LIKE operations using the String startsWith, endsWith and contains methods. For example, the lambda expression
person -> person.getAge() > 18 && person.getName().startsWith("Steve")
would translate to:
person.age > 18 AND person.name LIKE 'Steve%'

Most common SQL functions are supported as well. For example, person -> person.getBirthDate().getYear() will yield YEAR(person.birthDate).
person -> SqlFunctions.sum(person.getAge()) will yield SUM(person.age)

Lambda2Sql also automatically escapes table names and columns with backticks (`). If you do not wish this, you can specify it as an argument in the Lambda2Sql.toSql() method.

Feel free to open an issue with any requests you might have.

Install

You can include the Maven dependency:

<dependency>
    <groupId>com.github.collinalpert</groupId>
    <artifactId>lambda2sql</artifactId>
    <version>2.5.0</version>
</dependency>

Or add the JAR to your project.