fix a diagram and add alt text
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@ -934,16 +934,17 @@ An association between entity classes may be either:
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- _unidirectional_, navigable from `E` to `F` but not from `F` to `E`, or
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- _bidirectional_, and navigable in either direction.
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In this diagram, we can see the sorts of associations which are possible.
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In this example data model, we can see the sorts of associations which are possible:
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image::images/associations.png[]
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image::images/associations.png[Example data model,align="center",pdfwidth=90%]
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[TIP]
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// .One-to-one associations and subtyping
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====
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An astute observer of the diagram above might notice that the relationships we've represented as unidirectional one-to-one associations could reasonably be represented in Java using subtyping.
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An astute observer of the diagram above might notice that the relationship we've presented as a unidirectional one-to-one association could reasonably be represented in Java using subtyping.
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This is quite normal.
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A one-to-one association is the usual way we implement subtyping in a fully-normalized relational model.
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It's related to the `JOINED` <<mapping-inheritance,inheritance mapping>> strategy.
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====
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There are three annotations for mapping associations: `@ManyToOne`, `@OneToMany`, and `@ManyToMany`.
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@ -48,7 +48,7 @@ Thus, an entity instance may be in one of three states with respect to a given p
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2. _persistent_ — currently associated with the persistence context, or
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3. _detached_ — previously persistent in another session, but not currently associated with _this_ persistence context.
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image:images/entity-lifecyle.png[width=800,align="center"]
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image::images/entity-lifecyle.png[Entity lifecycle,width=800,align="center"]
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At any given moment, an instance may be associated with at most one persistence context.
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@ -57,7 +57,7 @@ We can think of the API of Hibernate in terms of three basic elements:
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- a _native API_ exposing the full set of available functionality, centered around the interfaces `SessionFactory`, which extends `EntityManagerFactory`, and `Session`, which extends `EntityManager`, and
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- a set of _mapping annotations_ which augment the O/R mapping annotations defined by JPA, and which may be used with the JPA-defined interfaces, or with the native API.
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image::images/api-overview.png[width=700,align="center"]
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image::images/api-overview.png[API overview,width=700,align="center"]
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As an application developer, you must decide whether to:
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@ -108,7 +108,7 @@ fundamental rule of thumb in ORM is:
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of a session/transaction, and fetch it immediately in one or two queries,
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- and only then start navigating associations between persistent entities.
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image:images/fetching.png[width=700,align="center"]
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image::images/fetching.png[Fetching process,width=700,align="center"]
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Without question, the most common cause of poorly-performing data access
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code in Java programs is the problem of _N+1 selects_. Here, a list of N
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