From 089d71c619cab156b405b9af51d38cb0d8b826db Mon Sep 17 00:00:00 2001 From: Gavin Date: Sun, 14 May 2023 05:08:11 +0200 Subject: [PATCH] add some words --- .../main/asciidoc/introduction/Entities.adoc | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/documentation/src/main/asciidoc/introduction/Entities.adoc b/documentation/src/main/asciidoc/introduction/Entities.adoc index 9dd2c38aab..97c886270f 100644 --- a/documentation/src/main/asciidoc/introduction/Entities.adoc +++ b/documentation/src/main/asciidoc/introduction/Entities.adoc @@ -971,7 +971,7 @@ That said, it's not a hard requirement to update the unowned side, at least if y [TIP] // .Unidirectional `@OneToMany`? ==== -In principle Hibernate _does_ allow you to have a unidirectional one to many, that is, a `@OneToMany` with no matching `@ManyToOne` on the other side. +In principle Hibernate _does_ allow you to have a unidirectional one-to-many, that is, a `@OneToMany` with no matching `@ManyToOne` on the other side. In practice, this mapping is unnatural, and just doesn't work very well. Avoid it. ==== @@ -1005,12 +1005,12 @@ In hindsight, we could have done more to make clear that this was always a viabl [[one-to-one-fk]] === One-to-one (first way) -The simplest sort of one-to-one association is almost exactly line a `@ManyToOne` association, except that it maps to a foreign key column with a `UNIQUE` constraint. +The simplest sort of one-to-one association is almost exactly like a `@ManyToOne` association, except that it maps to a foreign key column with a `UNIQUE` constraint. [TIP] // .One-to-many join table mappings ==== -Later, we'll see how to map a many-to-one association to an <>. +Later, we'll see how to map a one-to-one association to an <>. ==== A one-to-one association must be annotated `@OneToOne`: @@ -1055,6 +1055,8 @@ class Person { } ---- +`Person.author` is the unowned sure, because it's the side marked `mappedBy`. + .Lazy fetching for one-to-one associations **** Notice that we did not declare the unowned end of the association `fetch=LAZY`. @@ -1098,7 +1100,11 @@ class Author { } ---- -Notice that the `@Id` attribute is no longer a `@GeneratedValue` and, instead, the `author` association is annotated `@MapsId`. +Notice that, compared with the previous mapping: + +- the `@Id` attribute is no longer a `@GeneratedValue` and, +- instead, the `author` association is annotated `@MapsId`. + This lets Hibernate know that the association to `Person` is the source of primary key values for `Author`. Here, there's no extra foreign key column in the `Author` table, since the `id` column holds the identifier of `Person`. @@ -1194,6 +1200,8 @@ So we may expand our taxonomy with: | Collection of embeddable elements | Non-entity | Zero or more | `@ElementCollection Set names` |=== +There's actually two new kinds of mapping here: `@Array` mappings, and `@ElementCollection` mappings. + [CAUTION] // .These sorts of mappings are overused ==== @@ -1208,6 +1216,8 @@ The features we're about to meet in the next two subsections are used much more So if you're a beginner, you'll save yourself same hassle by staying away from these features for now. ==== +We'll talk about `@Array` mappings first. + [[arrays]] === Collections mapped to SQL arrays