Add immutable entity operator

[wreulicke]

Implements #74.

This PR provides to support immutable entity.

Below entity code works due to this PR.

public class Subscription {

 	@PrimaryKey(generationType=GenerationType.APPLICATION)
	public final Long int userId;

	public UserInfo(@Column(name = "userId") Long userId) {
		this.userId = userId;
	}
}

How do you think of this PR?

This PR contains potentially breaking changes...

[aadrian]

@wreulicke why does it have to be breakable?

[takezoe]

@aadrian What does "breakable" mean?

[wreulicke]

@aadrian
This diff into DefaultPropertyExtractor is related

this PR changes behavior with codes like below.

public class Subscription {
    // this property has getter/setter
    private String property.

    // this property has no getter/setter.
    private String transientProperty
}

The transientProperty in above codes will be recognized/extracted as property by this PR if use DefaultPropertyOperator.
But before, not recognized/extracted.
If recognized/extracted as property, mirage will persist it as column.
(This will cause a SQLException.)

So, I say "This PR contains potentially breaking changes..."

[takezoe]

This PR contains potentially breaking changes...

Ah, I overlooked this comment in the pull request. I think the immutable entity is good. But we need a way to keep the current behavior in case users need it.

By the way, userId in the first example should be final to be immutable like below?

public class Subscription {

 	@PrimaryKey(generationType=GenerationType.APPLICATION)
	public final Long userId;

	public UserInfo(@Column(name = "userId") Long userId) {
		this.userId = userId;
	}
}

[wreulicke]

By the way, userId in the first example should be final to be immutable like below?

great! fix it.

[wreulicke]

Ah, I overlooked this comment in the pull request. I think the immutable entity is good. But we need a way to keep the current behavior in case users need it.

Thanks for your review. I agree with you.

I close this PR now, and i will send PR to add test for keep compatibility.
Please review if recreate PR for immutable entity, Thanks.

[aadrian]

@wreulicke also please consider the Map support, since this is also a very important feature.

[wreulicke]

also please consider the Map support, since this is also a very important feature.

@aadrian Thanks for your review.
I will consider also.

By the way, Why do you think that the Map support is important?
For Clojure? 😆

[aadrian]

@wreulicke yes indeed, for Clojure too, for Groovy, and also for dynamic tooling (like ETL) that can't use classes, since stuff needs to be dynamic.