DATAJPA-218 - Support extracting parameters from a bean parameter.

[thomasdarimont]

Added prototypic support for query by example queries to
SimpleJpaRepositories. Clients can use an Example Object to
wrap an existing prototype entity instance that will be used to
derive a query from.
The example wrapper allows us to customize the parameter extraction / generation
from the provided prototype bean.

Would be great if we could unify this effort with the infrastructure
from DATAMONGO-1245.

[thomasdarimont]

Potential things to improve / think about are:

• Provide a common shared Example wrapper in Spring Data Commons.
• Support nested attribute paths for exclusion.
• Consider an alternative style to express example predicates:

 userRepository.findByExample(new Example(){
    String name = "thomas";
    String countryCode = "de";
    Boolean tired = true;
});

//or perhaps

 userRepository.findByAttributes(new Attrbutes(){
    String name = "thomas";
    String countryCode = "de";
    boolean tired = true;
});

• Provide query by example at CrudRepository level.

[ripper2hl]

Why no accept this pull request?, better approach ? , the querys by Example its a great feature 👍

[schauder]

This is superseeded by #164