All about Fetch Models

Introduction

A fetch model represents a graph that describes the shape of an entity to be fetched.

Fetch Categories

An essential component of a fetch model is its category, which defines a set of properties that are implicitly included in a fetch model.

Fecth categories are defined by ua.com.fielden.platform.entity.query.fluent.fetch.FetchCategory.

Description of each category follows, with the categories ordered by richness, ascendingly (the last category includes the most properties).

• NONE - nothing is included.
• ID_ONLY - sole property id is included.
• ID_AND_VERSION - a slightly broader fetch model than ID_ONLY.
  • id is included if it belongs to the entity type;
  • version is included if the entity type is persistent;
  • refCount and active are included if entity type is activatable;
  • the group of "last updated by" properties is included if the entity type is persistent and has those properties.
• DEFAULT - equivalent to ALL but with narrower sub-fetch models - only simple keys and key members will have a sub-fetch model other than ID_ONLY.
• KEY_AND_DESC
  • key is included;
  • desc is included if it belongs to the entity type.
  • all of ID_AND_VERSION are included if the entity type is persistent;
• ALL - includes all retrievable properties, except the following:
  • collectional properties are excluded;
  • non-retrievable properties are excluded;
  • calculated properties are excluded (unless they have a component type).
• ALL_INCL_CALC (all, including calculated) - equivalent to ALL but also includes calculated properties.

API

Core abstractions for fetch models in the platform code are:

• ua.com.fielden.platform.entity.fetch.IFetchProvider - application developer facing API, used for Web UI and entity companions.
• ua.com.fielden.platform.entity.query.fluent.fetch - application developer facing API, used for EQL queries.
• ua.com.fielden.platform.entity.query.IRetrievalModel - internal representation, used by the EQL engine.

Fetching sub-properties of a component type

TG version 2.0.0 Fetching of standalone sub-properties of a component type is unsupported. The whole component-typed property must be fetched.

For example, let Note be an entity with property text: RichText.

fetch1 = fetchNone(Note.class).with("text.coreText");
fetch2 = fetchNone(Note.class).with("text");

query = select(Note.class).yieldAll().modelAsEntity(Note.class);

Then, query with fetch1 will produce notes with property text proxied, while with fetch2 - all components of RichText will be retrieved and text will be assigned a corresponding value.

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