[hibernate-dev] [BV] Path, string or object model

[Emmanuel Bernard]

Please review and comment.

Begin forwarded message:

From: Emmanuel Bernard <emmanuel.bern...@jboss.com>
Date:  June 17, 2009 14:41:03  EDT
To:
Subject: Re: Path, string or object model

Here is the solution I cooked. I think it's acceptable but add some complexity in the ConstraintValidatorContext API (see other email). Please review (pay special attention to the examples).

A Path represents the path and is the one accepted by the path consuming APIs. A Path is an Iterable of Nodes.

/**
 * Represent a navigation path from an object to another.
 * Each path element is represented by a Node.
 *
 * The path corresponds to the succession of nodes
 * in the order they are retured by the Iterator
 *
 * @author Emmanuel Bernard
 */
public interface Path extends Iterable<Node> {
}


A node represent a path element.

/**
 * Represents an element of a navigation path
 *
 * @author Emmanuel Bernard
 */
public interface Node {
        /**
         * Property name the node represents
         * or null if the leaf node and representing an entity
         * (in particular the node representing the root object
         * has its name null)
         */
        String getName();

        /**
         * True if the node represents an object contained in an Iterable
         * or in a Map.
         */
        boolean isInIterable();

        /**
         * The index the node is placed in if contained
         * in an array or List. Null otherwise.
         */
        Integer getIndex();

        /**
         * The key the node is placed in if contained
         * in a Map. Null otherwise.
         */
        Object getKey();
}

A few interesting points:
 - the index / key is hosted by the node after the collection node

Here are a few examples and their Node equivalent

""
0: Node(name:null, isInIterable:false, index:null, key:null)

"email"
0: Node(name:email, isInIterable:false, index:null, key:null)

"addresses"
0: Node(name:addresses, isInIterable:false, index:null, key:null)

"addresses["home"]" represent the bean level of an Address object
0: Node(name:addresses, isInIterable:false, index:null, key:null)
1: Node(name:null, isInIterable:true, index:null, key:home)

"addresses["home"].city"
0: Node(name:addresses, isInIterable:false, index:null, key:null)
1: Node(name:city, isInIterable:true, index:null, key:home)

"billingAddresses[3].country.name"

0: Node(name:billingAddresses, isInIterable:false, index:null, key:null)

1: Node(name:country, isInIterable:true, index:3, key:null)
2: Node(name:name, isInIterable:false, index:null, key:null)


ConstraintViolation renders a Path

public interface ConstraintViolation<T> {
    Path getPropertyPath();
}

TraversableResolver accepts a path

public interface TraversableResolver {
        boolean isReachable(Object traversableObject,
                                                  String traversableProperty,
                                                  Class<?> rootBeanType,
                                                  Path pathToTraversableObject,
                                                  ElementType elementType);
    ...
}

PS: should String traversableProperty be Node traversableProperty ?


On  May 27, 2009, at 12:19, Emmanuel Bernard wrote:

In several areas we do describe path:
 - ConstraintViolation

- ConstraintValidatorContext (with addError(String, String) which allows to concatenate substrings

So far we use the notion of string to represent it
 - address.name
 - cards[3].color
 - addresses["home"].city

I have added the idea of using [] for simple Iterable objects (ie non indexed, like a Set)

 - accounts[].balance

Anybody objects to that?

Second point
Do we want to replace this String approach with a path object mode?

http://opensource.atlassian.com/projects/hibernate/browse/BVAL-143
______

path are today strings with dot separating properties. But it break when Set or Iterable are used.

We could replace that with
--- First strawman, must evolve --
class PathElement {
  String getName();
  PathElement getParentPath();
  boolean isIterable();
  boolean isIndexed();
  Object getIndex();
  //TODO int getIndex()?

// not happy about that as it is only useful for Constraintciolation

  PathElement getChild();
}

PathElement would be used for Constraintvuilation, maybe CVContext etc

can this be refactored using inheritance + generics to have an IndexedPathElement only when it matters (probably no unfortunately)

______


Pros:

- less string manipulation by the user and the TraversableResolver implementation - the map index no longer rely on "[" + toString() + "]" and is likely more easily handled

Cons:

- ConstraintValidatorContext becomes more complex as it needs to expose some kind of path element builder. - we would like need to standardize some kind of String serialization anyway

 - I don't see Pros as huge advantages

WDYT?

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