[hibernate-issues] [JIRA] (HSEARCH-3903) Filters based exclusively on mapper metadata for @IndexedEmbedded

[Yoann Rodière (JIRA)]

Yoann Rodière ( https://hibernate.atlassian.net/secure/ViewProfile.jspa?accountId=557058%3A58fa1ced-171a-4c00-97e8-5d70d442cc4b ) *updated* an issue

Hibernate Search ( https://hibernate.atlassian.net/browse/HSEARCH?atlOrigin=eyJpIjoiYTZjNWQyMDZlNWI4NGIwNmE0OTIyY2VhYmJiMWQ2NDEiLCJwIjoiaiJ9 ) / New Feature ( https://hibernate.atlassian.net/browse/HSEARCH-3903?atlOrigin=eyJpIjoiYTZjNWQyMDZlNWI4NGIwNmE0OTIyY2VhYmJiMWQ2NDEiLCJwIjoiaiJ9 ) HSEARCH-3903 ( https://hibernate.atlassian.net/browse/HSEARCH-3903?atlOrigin=eyJpIjoiYTZjNWQyMDZlNWI4NGIwNmE0OTIyY2VhYmJiMWQ2NDEiLCJwIjoiaiJ9 ) Filters based exclusively on mapper metadata for @IndexedEmbedded ( https://hibernate.atlassian.net/browse/HSEARCH-3903?atlOrigin=eyJpIjoiYTZjNWQyMDZlNWI4NGIwNmE0OTIyY2VhYmJiMWQ2NDEiLCJwIjoiaiJ9 )

Change By: Yoann Rodière ( https://hibernate.atlassian.net/secure/ViewProfile.jspa?accountId=557058%3A58fa1ced-171a-4c00-97e8-5d70d442cc4b )

The {{includePaths}} filter in {{@IndexedEmbedded}} refers to index field paths. This has several drawbacks:

* Part of the implementation has to be in the backend, which feels quite dirty.
* This is not very consistent with the {{maxDepth}} filter, which applied to the {{@IndexedEmbedded}} only (depth of fields created within an included bridge is unlimited).
* The filters cannot easily be applied to dynamic fields, so dynamic fields are always included as soon as their nearest static parent is included.
* The filter can end up including some fields declared by a custom field bridge, but not others.
** This does not make sense performance-wise as the fields will still be populated by the bridge, but ignored by the backend.
** Worse, when we introduce support for bridge-defined predicates (HSEARCH-3320), we may end up with dysfunctional predicates because only some fields are present, while the bridge expects all fields to be present.
* We are forced to use inference to detect which bridges should be included or excluded, based on the fields they declared.
** This code is unnecessarily complex.
** This code does not work correctly with field templates, since we cannot know in advance whether dynamic fields will be included. In particular:
*** Bridges that declare field templates, but only ever add dynamic fields that would not match the {{includePaths}}, are included nonetheless.
*** Bridges that do not declare anything and rely on field templates declared by a parent (which is legal) are excluded.

We could get rid of most of the complexity by implementing filters differently, based on mapper metadata exclusively (mapping annotations and/or entity model).

h3. Solution 1: property paths

We could rely on property paths instead of field paths. Only bridges applied to included properties are themselves included.

The major drawback is that there wouldn't be any way to filter out type bridges.

h3. Solution 2: groups

We could rely on "groups", similarly to the {{@LazyGroup}} support in Hibernate ORM, or to the group support in Hibernate Validator.

One assigns groups to every {{@Field}}/{{@IndexedEmbedded}}, then references the groups in {{@IncludedEmbedded(includeGroups = ...)}}.

The main problem with this solution is its complexity; Validator is using groups and I know they can be pretty complex to handle. We should definitely see what makes them so complex in Validator to avoid the same problems in Search.

For example:

{code}
@Indexed
public class Level1Entity {

// Will include id only
@IndexedEmbedded
private Level2Entity level2_1;

// Will include id, name
@IndexedEmbedded(includeGroups = {BuiltinGroups.DEFAULT, "base"})
private Level2Entity level2_2;

// Will include id, name, category
@IndexedEmbedded(includeGroups = {BuiltinGroups.DEFAULT, "base", "advanced"})
private Level2Entity level2_3;

}

public class Level2Entity {

@GenericField // Default group
private String id;

@GenericField(groups = "base")
private String name;

@GenericField(groups = "advanced")
private String category;

}
{code}

h4. Variation: overriding {{includeGroups}}

It would prevent us from supporting the use case mentioned in HSEARCH-1112 directly, but I believe the same effect could be achieved if we defined group filters as "overriding" instead of "composable": an {{@IndexedEmbedded(includeGroups = "a")}} that includes an {{@IndexedEmbedded(includeGroups = "b")}} would just act as if the contained {{@IndexedEmbedded}} included group "a", and only group "a".

For example:

{code}
@Indexed
public class Level1Entity {

// Will include level2.level3.a only
@IndexedEmbedded(includeGroups = "a")
private Level2Entity level2;

}

public class Level2Entity {

@GenericField(groups = "b")
private String name;

@IndexedEmbedded(includeGroups = "b") // includeGroups is overridden in Level1Entity
private String id;

}

public class Level3Entity {

@GenericField(groups = "a")
private String a;

@GenericField(groups = "b")
private String b;

}
{code}

There are pros and cons:

* Pro: Groups may be easier to implement and understand: the various filters defined in indexed-embedded entities would no longer be relevant. One could argue that it's the opposite, though: the fact that filters defined in indexed-embedded entities are ignored can be confusing.
* Con: it would become harder to manage cycles through group filtering: you would no longer be able to rely on indexed-embedded entities to filter out cycles through groups (since their group filters are ignored).
* Con: the behavior would not be consistent with that of {{maxDepth}}.

h3. Next

h4. Deprecation

As a second step, we should probably deprecate {{includePaths}} and mark it for removal in a later major version (7+).

h4. Going further: dynamic group selection

One could imagine to allow selecting groups dynamically. All the groups that *can* be selected would be included in the index schema, and when indexing some fields would get enabled or not based on the dynamic group selection.

This would provide a feature similar to the {{AlternativeBinder}}, but much more powerful.

There is one unknown, though: how would {{@IndexedEmbedded.includeGroups}} interact with the dynamic group selection? If dynamic group selection is overridden by {{@IndexedEmbedded.includeGroups}}, it will likely not work as intended for the "multi See HSEARCH - language" use case of {{AlternativeBinder}} 3971. If dynamic group selection ignores {{@IndexedEmbedded.includeGroups}}, it will become impossible to exclude dynamically enabled fields from {{@IndexedEmbedded}}.

Maybe we should separate the two concepts, e.g. {{@GenericField(groups = ..., dynamicGroups = ...)}}?

Or maybe we should assign a static group to the "dynamic group resolver": the resolver and all corresponding fields would be included in the schema if the resolver's assigned static group is included, even if the field's (dynamic) groups are not included. Then it would be the user's responsibility to make sure static and dynamic groups use different names, so as not to include dynamic groups statically by mistake.

h4. Going further: using field groups to select fields in the search DSL

We could address HSEARCH-3926 by contributing groups to the index metamodel: {{@GenericField(groups = "foo")}} would assign the group "foo" to the corresponding index field, which could then be targeted at query time by selecting the group "foo". See HSEARCH-3926 for more information.

This would be a reasonable use of groups, I believe?

( https://hibernate.atlassian.net/browse/HSEARCH-3903#add-comment?atlOrigin=eyJpIjoiYTZjNWQyMDZlNWI4NGIwNmE0OTIyY2VhYmJiMWQ2NDEiLCJwIjoiaiJ9 ) Add Comment ( https://hibernate.atlassian.net/browse/HSEARCH-3903#add-comment?atlOrigin=eyJpIjoiYTZjNWQyMDZlNWI4NGIwNmE0OTIyY2VhYmJiMWQ2NDEiLCJwIjoiaiJ9 )

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