@UniqueConstraints 不适用于 @JoinTable

Question

我正在使用 Playframework 1.2.4 和 PostgresSQL 9.1.2。我有以下实体：Recipe 和 RecipeItem。一个Recipe 有一组RecipeItems。我在 Recipe 类中对一组配方项进行了如下注释：

@Required
@MinSize(1)
@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
@JoinTable( name = "RecipeItemForIngredients",
joinColumns = @JoinColumn(name = "recipeId"),
inverseJoinColumns = @JoinColumn(name = "recipeItemId"),
uniqueConstraints = @UniqueConstraint(name = "uq_recipeItemPerRecipe",
columnNames = {"recipeId", "recipeItemId"}))
public Set<RecipeItem> items = Sets.newHashSet();

但是当我检查 PgAdmin 以查看约束是否已应用于 RecipeItemForIngredients 表时，我找不到它。这就是 PgAdmin 显示的内容。

CREATE TABLE recipeitemforingredients
(
  recipeid bigint NOT NULL,
  recipeitemid bigint NOT NULL,
  CONSTRAINT recipeitemforingredients_pkey PRIMARY KEY (recipeid, recipeitemid),
  CONSTRAINT fk5ac547a883708db FOREIGN KEY (recipeid)
      REFERENCES recipe (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT fk5ac547ad6e1da8f FOREIGN KEY (recipeitemid)
      REFERENCES "recipe$recipeitem" (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT recipeitemforingredients_recipeitemid_key UNIQUE (recipeitemid)
)

有谁知道为什么会发生这种情况？也许 Playframework 使用的 ORM 不支持这个注解。

Answer 1

这个约束没有多大意义，而且默认情况下你有一个更强的约束：

CONSTRAINT recipeitemforingredients_recipeitemid_key UNIQUE (recipeitemid)

如果recipeItemId是唯一的，那么元组(recipeId, recipeItemId)当然也是唯一的。

另外，由于表的PK是(recipeId, recipeItemId)，所以该约束已经被PK约束应用了。