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About wq.db's Design Patterns

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About wq.db's Design Patterns

wq.db.patterns

To promote long term sustainability in data management projects, wq.db includes a number of re-usable design patterns that facilitate the creation of flexible database layouts. These patterns are designed to be integrated with your existing data structures, and are implemented as installable Django apps.

Each of the included design patterns provides a small set of Django models in a schema similar to the Entity-Attribute-Value (EAV) data model. For example, the annotate pattern includes an AnnotationType model (the "Attribute") and an Annotation model (the "Value"). The Entity in each pattern defined as an abstract class (e.g. AnnotatedModel) which you can subclass with concrete models to leverage the annotate API.

These EAV-style data models are particularly useful for building field data collection apps where the parameters being collected may change over time (i.e. nearly all data collection apps). To add new parameter definitions, a project administrator can use a web interface (add rows), instead of needing to have a developer change the database schema (add columns).

For an in-depth discussion of EAV and the related ERAV data model, see Capturing Quality: Retaining Provenance for Curated Volunteer Monitoring Data. The vera project provides an implementation of ERAV, which has better support than EAV for time series and tracking multiple versions of data.

Each pattern is implemented as a separate Django app under wq.db.patterns. For convenience, wq.db.patterns.models includes references to all of the models defined in each respective pattern. For example, to use the annotate pattern:

# settings.py
INSTALLED_APPS = (
   # ...
   'wq.db.patterns.annotate'
)

# myapp/models.py
from django.db import models
from wq.db.patterns import models as patterns
class Report(patterns.AnnotatedModel):
   date = models.DateField()
   # ...

Patterns

model entity base class attribute model value model description
annotate AnnotatedModel AnnotationType Annotation Generic entity-attribute-value (EAV) implementation.
identify IdentifiedModel Authority Identifier Track entity identifiers assigned by multiple third party authorities
locate LocatedModel N/A Location Manage multifaceted geographic location data
mark MarkedModel MarkdownType Markdown Maintain multiple markdown snippets for a model (e.g. in different languages)
relate RelatedModel RelationshipType,
InverseRelationshipType
Relationship,
InverseRelationship
Generic typed many-to-many relationships

If none of the above provide quite what you need, you can also define your own EAV pattern by extending the base implementation. See Advanced Patterns for more information.