# Spring Data MongoDB - Query-by-Example (QBE) example

This project contains samples of Query-by-Example of Spring Data MongoDB.

## Support for Query-by-Example

Query by Example (QBE) is a user-friendly querying technique with a simple interface. It allows dynamic query creation and does not require to write queries containing field names. In fact, Query by Example does not require to write queries using JPA-QL at all.

An `Example` takes a data object (usually the entity object or a subtype of it) and a specification how to match properties. You can use Query by Example with `MongoOperations` and Repositories.

```java
public interface PersonRepository extends CrudRepository<Person, String>, QueryByExampleExecutor {
}
```

```java
Example<Person> example = Example.of(new Person("Jon", "Snow"));
repo.findAll(example);


ExampleMatcher matcher = ExampleMatcher.matching().
    .withMatcher("firstname", endsWith())
    .withMatcher("lastname", startsWith().ignoreCase());

Example<Person> example = Example.of(new Person("Jon", "Snow"), matcher); 
repo.count(example);
```

This example contains two test classes to illustrate Query-by-Example with `MongoOperations` in `MongoOperationsIntegrationTests` and the usage with a Repository in `UserRepositoryIntegrationTests`.