Hibernate HQL：获取结果的数量而不实际返回它们 [英] Hibernate HQL: Get count of results without actually returning them

问题描述

我想获得动态生成的HQL查询结果的计数，但实际上并没有得到结果列表。说我的查询是这样的：

  select公司LEFT OUTER JOIN FETCH产品产品
  

我在Hibernate文档中读到：

<您可以计算查询结果的数量而不返回它们：

 （（Integer） session.createQuery（select count（*）from ....）。iterate（）。next（））.intValue（）
  

我怀疑我应该用我的查询替换 .... ，但这不起作用，因为HQL不支持FROM中的子选择。 / p>

那么，我该如何计算动态生成的HQL查询的结果呢？我认为通过执行它并获得结果列表的.size（）可能是不必要的开销。

干杯！

**更新：**

我用这个正则表达式转换我的查询：

  Number num =（Number）em.createQuery（dynamicQuery.replaceAll（select \\w + from，select count（*）from））。getSingleResult（）; 
  

我得到这个：

Blockquote

EJB异常：嵌套的异常是：java.lang.IllegalArgumentException：org.hibernate.QueryException：查询指定的连接读取，但获取的关联的所有者不在选择列表中[FromElement {显式，不是集合连接，fetch连接，fetch非连接-lazy属性，classAlias = product，role = org.myCompany.applicant.entity.Applicant.products，tableName = PRS_DEV.PRODUCT，tableAlias = products1_，origin = PRS_DEV.APPLICANT applicant0_，colums = {applicant0_.APPLICANT_ID，className = org。 myCompany.product.entity.Product}}] [从org.myCompany.applicant.entity.Applicant申请人选择count（）申请人LEFT OUTER JOIN FETCH申请人。产品];嵌套的异常是：java.lang.IllegalArgumentException：org.hibernate.QueryException：查询指定的连接读取，但获取的关联的所有者不在选择列表中[FromElement {显式，不是集合连接，fetch连接，fetch非连接-lazy属性，classAlias = product，role = org.myCompany.applicant.entity.Applicant.products，tableName = PRS_DEV.PRODUCT，tableAlias = products1_，origin = PRS_DEV.APPLICANT applicant0_，colums = {applicant0_.APPLICANT_ID，className = org。 myCompany.product.entity.Product}}] [select count（）from org.myCompany.applicant.entity.Applicant申请人LEFT OUTER JOIN FETCH申请人。产品产品]

解决方案

这应该会有诀窍：

  select count（*）FROM公司c JOIN ... 
  

没有子选择，而不是返回公司，您返回计数。

编辑： FETCH



  org.myCompany.applicant.entity.Applicant应用程序中的select count（产品）
 LEFT OUTER JOIN申请人。产品产品
  




I want to get the count of the results of a dynamically-generated HQL query, without actually getting the list of results. Say that the query I have is something like:

select Company company LEFT OUTER JOIN FETCH products product

I read in the Hibernate documentation that:

You can count the number of query results without returning them:

( (Integer) session.createQuery("select count(*) from ....").iterate().next() ).intValue()

I suspected that I should be replacing the .... with my query, but that does not work, as HQL does not support sub-selects in FROM.

So, how should I count the results of a dynamically generated HQL query? I think that by executing it and getting the .size() of the results list may be unnecessary overhead.

Cheers!

**UPDATE: **

I used this regex to convert my query:

Number num = (Number) em.createQuery(dynamicQuery.replaceAll("select \\w+ from ", "select count(*) from ")).getSingleResult();

And I get this:

Blockquote

EJB Exception: ; nested exception is: java.lang.IllegalArgumentException: org.hibernate.QueryException: query specified join fetching, but the owner of the fetched association was not present in the select list [FromElement{explicit,not a collection join,fetch join,fetch non-lazy properties,classAlias=product,role=org.myCompany.applicant.entity.Applicant.products,tableName=PRS_DEV.PRODUCT,tableAlias=products1_,origin=PRS_DEV.APPLICANT applicant0_,colums={applicant0_.APPLICANT_ID ,className=org.myCompany.product.entity.Product}}] [select count() from org.myCompany.applicant.entity.Applicant applicant LEFT OUTER JOIN FETCH applicant.products product ]; nested exception is: java.lang.IllegalArgumentException: org.hibernate.QueryException: query specified join fetching, but the owner of the fetched association was not present in the select list [FromElement{explicit,not a collection join,fetch join,fetch non-lazy properties,classAlias=product,role=org.myCompany.applicant.entity.Applicant.products,tableName=PRS_DEV.PRODUCT,tableAlias=products1_,origin=PRS_DEV.APPLICANT applicant0_,colums={applicant0_.APPLICANT_ID ,className=org.myCompany.product.entity.Product}}] [select count() from org.myCompany.applicant.entity.Applicant applicant LEFT OUTER JOIN FETCH applicant.products product ]

解决方案

This should do the trick:

select count(*) FROM Company c JOIN ...

There is no sub-select involved, just instead of returning Company, you return the count.

Edit: The FETCH is out of place now. You're not returning the entities from the query, but only the count, thus, Hibernate complains. Removing it should help:

select count(product) from org.myCompany.applicant.entity.Applicant applicant 
    LEFT OUTER JOIN applicant.products product

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