在Hibernate中向列表添加投影

本文介绍了在Hibernate中向列表添加投影的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 我有一个名为Order的@Entity，我有一个名为orderEmails的字段或成员变量，如下所示。 @Entity @Table（name =order） public class Order { @Id @Column（name =order_int）私人长ID; @OneToMany（cascade = CascadeType.ALL，fetch = FetchType.LAZY） @JoinColumn（name =order_int，insertable = false，updatable = false） private List< ; OrderEmail> orderEmails; ... } 我试图在这个订单上创建Projections，这意味着我要从Order实体和OrderEmail实体中选择一些特定的列 但是，当我在orderEmails字段上创建一个投影。我没有收到完整的电子邮件列表。这是我想要的。这里是我尝试的代码 ProjectionList columnList = Projections.projectionList（）; ... columnList.add（Projections.property（id）。as（id））; ... columnList.add（Projections.property（orderemails.EmailAddress）。as（email））; 请注意，我也尝试了 columnList.add（Projections.property（orderemails ）。如（ 电子邮件））; 并将电子邮件（as）更改为List，但没有帮助 是否有可能在Hibernate中的List上创建投影？ 解决方案我猜hibernate没有提供这样的功能。要做到这一点，您将不得不使用数据库特定的功能，如Oracle的 LISTAGG 或 GROUP_CONCAT 。它会将所有电子邮件（字符串）分组到一个列表中，结果如下： ORDER_ID电子邮件 1 nemo @ email，dory @ email，whale @ email 2 spongebob @ email，squarepants @ email public List< Map>< p> ; emailsByOrder（）{ Criteria c = session.createCriteria（Order.class，order）; Criteria critEmail = c.createCriteria（orderEmails，emails）; String listAgg =LISTAGG（{别名} .EMAIL_ADDRESS_COLUMN_NAME，'，'）WITHIN GROUP（ORDER BY {别名} .EMAIL_ADDRESS_COLUMN_NAME ASC）AS EMAILS; critEmail.setProjection（Projections.projectionList（）。add（Projections.groupProperty（order.idOrder）。as（ORDER_ID）） .add（Projections.sqlProjection（listAgg，new String [ ] {EMAILS}，new Type [] {new StringType（）}）））; c.setResultTransformer（Transformers.ALIAS_TO_ENTITY_MAP）; return（List< Map>）c.list（）; } I have a @Entity called Order in this I have a field or a member variable called orderEmails as show below.@Entity@Table(name = "order")public class Order {@Id@Column(name = "order_int")private Long id;@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)@JoinColumn(name = "order_int", insertable = false, updatable = false)private List<OrderEmail> orderEmails;...}I am trying to create Projections on this Order , meaning I want to select some specific columns from the Order entity and a column from the OrderEmail entityBut, when I create a projection on the orderEmails field. I don't get the complete list of emails. Which is what I want. Here is the code that I am tryingProjectionList columnList = Projections.projectionList();...columnList.add(Projections.property("id").as("id"));...columnList.add(Projections.property("orderemails.EmailAddress").as("email"));Note, I have also triedcolumnList.add(Projections.property("orderemails").as("email"));and changed the email (in as) to be a List, but didn't helpIs it possible to create a projection on a List in Hibernate ? 解决方案 I guess hibernate does not provide such a function. To do this you will have to use database specific functions like LISTAGG from Oracle or GROUP_CONCAT from MySQL. It will group all emails (the String) into one colum, so the result would be:ORDER_ID EMAILS1 nemo@email, dory@email, whale@email2 spongebob@email, squarepants@emailYou can use database specific functions in Hibernate with sqlProjection, so the code will look something like this:public List<Map> emailsByOrder(){ Criteria c = session.createCriteria(Order.class,"order"); Criteria critEmail = c.createCriteria("orderEmails", "emails"); String listAgg = "LISTAGG({alias}.EMAIL_ADDRESS_COLUMN_NAME, ', ') WITHIN GROUP(ORDER BY {alias}.EMAIL_ADDRESS_COLUMN_NAME ASC) AS EMAILS"; critEmail.setProjection(Projections.projectionList().add(Projections.groupProperty("order.idOrder").as("ORDER_ID")) .add(Projections.sqlProjection(listAgg, new String[]{"EMAILS"}, new Type[]{new StringType()}))); c.setResultTransformer(Transformers.ALIAS_TO_ENTITY_MAP); return (List<Map>) c.list();} 这篇关于在Hibernate中向列表添加投影的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！