blocks|key|2851925|text|显然，作为查询的计数的数字：)它的类型按规范是Long。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2851926|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Obviously, a number which is the count from the query:) Its type by specification is Long.

blocks|key|945795|text|AFAIK+COUNT函数返回Long|type|unstyled|depth|inlineStyleRanges|entityRanges|data|945796|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

AFAIK COUNT function returns Long

blocks|key|943679|text|根据JPA+specification，COUNT返回一个长整型：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|943680|943681|+4.8.4+SELECT子句中的聚合函数查询结果|blockquote|943682|943683|可以是应用于路径表达式的聚合函数的结果。|943684|可以在查询的SELECT子句中使用以下聚合函数:+AVG、COUNT、MAX、MIN、SUM。|943685|对于除COUNT之外的所有聚合函数，作为聚合函数的参数的路径表达式必须在状态字段中终止。COUNT的路径表达式参数可以在状态字段或关联字段中终止，或者COUNT的参数可以是标识变量。|943686|函数SUM和AVG的参数必须是数字。函数MAX和MIN的参数必须对应于可排序的状态字段类型(即数字类型、字符串类型、字符类型或日期类型)。|943687|使用聚合函数的查询结果中包含的Java类型如下：|943688|943689|943690|COUNT返回Long.|unordered-list-item|style|BOLD|943691|MAX，MIN返回它们所应用到的状态字段的类型。|943692|AVG返回Double。|943693|SUM在应用于整型类型(不包括BigInteger+)的状态字段时返回Long；在应用于浮点类型的状态字段时返回Double；在应用于BigInteger类型的状态字段时返回BigInteger；在应用于BigDecimal类型的状态字段时返回BigDecimal。|943694|943695|如果使用SUM、AVG、MAX或MIN，并且没有可应用聚合函数的值，则聚合函数的结果为NULL。|943696|如果使用了COUNT，并且没有可以应用COUNT的值，则聚合函数的结果为0。|943697|聚合函数的参数前面可以有关键字DISTINCT，以指定在应用聚合函数之前要消除重复的值。|943698|无论是否指定了关键字DISTINCT，都会在应用聚合函数之前消除NULL值。|943699|entityMap|0|LINK|mutability|MUTABLE|url|https://download.oracle.com/otndocs/jcp/ejb-3_0-fr-eval-oth-JSpec/^0|2|H|0|0|0|0|0|0|0|0|0|0|0|0|0|C|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1M|8|@]|9|@$A|1N|B|1O|1|1P]]|C|$]]|$1|D|3|-4|5|6|7|1Q|8|@]|9|@]|C|$]]|$1|E|3|F|5|G|7|1R|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|1S|8|@]|9|@]|C|$]]|$1|I|3|J|5|6|7|1T|8|@]|9|@]|C|$]]|$1|K|3|L|5|6|7|1U|8|@]|9|@]|C|$]]|$1|M|3|N|5|6|7|1V|8|@]|9|@]|C|$]]|$1|O|3|P|5|6|7|1W|8|@]|9|@]|C|$]]|$1|Q|3|R|5|6|7|1X|8|@]|9|@]|C|$]]|$1|S|3|-4|5|6|7|1Y|8|@]|9|@]|C|$]]|$1|T|3|-4|5|6|7|1Z|8|@]|9|@]|C|$]]|$1|U|3|V|5|W|7|20|8|@$A|21|B|22|X|Y]]|9|@]|C|$]]|$1|Z|3|10|5|W|7|23|8|@]|9|@]|C|$]]|$1|11|3|12|5|W|7|24|8|@]|9|@]|C|$]]|$1|13|3|14|5|W|7|25|8|@]|9|@]|C|$]]|$1|15|3|-4|5|6|7|26|8|@]|9|@]|C|$]]|$1|16|3|17|5|6|7|27|8|@]|9|@]|C|$]]|$1|18|3|19|5|6|7|28|8|@]|9|@]|C|$]]|$1|1A|3|1B|5|6|7|29|8|@]|9|@]|C|$]]|$1|1C|3|1D|5|6|7|2A|8|@]|9|@]|C|$]]|$1|1E|3|-4|5|6|7|2B|8|@]|9|@]|C|$]]]|1F|$1G|$5|1H|1I|1J|C|$1K|1L]]]]

As per the <a href="https://download.oracle.com/otndocs/jcp/ejb-3_0-fr-eval-oth-JSpec/" rel="noreferrer">JPA specification</a>, COUNT returns a Long:

<blockquote>
 <h3>4.8.4 Aggregate Functions in the SELECT Clause The result of a query</h3>
 
 may be the result of an aggregate
 function applied to a path expression.
 
 The following aggregate functions can
 be used in the SELECT clause of a
 query: AVG, COUNT, MAX, MIN, SUM.
 
 For all aggregate functions except
 COUNT, the path expression that is the
 argument to the aggregate function
 must terminate in a state-field. The
 path expression argument to COUNT may
 terminate in either a state-field or a
 association-field, or the argument to
 COUNT may be an identification
 variable.
 
 Arguments to the functions SUM and AVG
 must be numeric. Arguments to the
 functions MAX and MIN must correspond
 to orderable state-field types (i.e.,
 numeric types, string types, character
 types, or date types).
 
 The Java type that is contained in the
 result of a query using an aggregate
 function is as follows:
 
 <ul>
 <li>COUNT returns Long.</li>
 <li>MAX, MIN return the type of the state-field to which they are applied.</li>
 <li>AVG returns Double.</li>
 <li>SUM returns Long when applied to state-fields of integral types (other
 than BigInteger); Double when applied
 to state-fields of floating point
 types; BigInteger when applied to
 state-fields of type BigInteger; and
 BigDecimal when applied to
 state-fields of type BigDecimal.</li>
 </ul>
 
 If SUM, AVG, MAX, or MIN is used, and
 there are no values to which the
 aggregate function can be applied, the
 result of the aggregate function is
 NULL.
 
 If COUNT is used, and there are no
 values to which COUNT can be applied,
 the result of the aggregate function
 is 0.
 
 The argument to an aggregate function
 may be preceded by the keyword
 DISTINCT to specify that duplicate
 values are to be eliminated before the
 aggregate function is applied.
 
 Null values are eliminated before the
 aggregate function is applied,
 regardless of whether the keyword
 DISTINCT is specified.
</blockquote>

blocks|key|1688228|text|COUNT(t)专门返回java.lang.Long。当它在这个上下文中单独出现时，它会按原样返回。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1688229|(在其他上下文中，COUNT生成的Long可能是包装的，但不是今天。)|1688230|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

COUNT(t) specifically returns java.lang.Long. When its appears on its own in this context it is returned as-is. 

(In other contexts the Long generated by COUNT may be wrapped, but not today.)

blocks|key|945949|text|注意：JQPL和原生查询之间存在差异|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|945950|Query+query+=+em.createQuery("SELECT+COUNT(p)+FROM+PersonEntity+p+"+);|code-block|syntax|javascript|945951|java.lang.Long+-->+query.getSingleResult().getClass().getCanonicalName()|CODE|945952|Query+query+=+em.createNativeQuery("SELECT+COUNT(*)+FROM+PERSON+"+);|945953|java.math.BigInteger+-->+query.getSingleResult().getClass().getCanonicalName()|945954|entityMap^0|3|4|8|2|0|0|0|E|J|1H|0|0|0|K|P|1H|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|M]]|D|@]|E|$]]|$1|N|3|O|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|P|3|Q|5|6|7|15|8|@$9|16|A|17|B|C]|$9|18|A|19|B|M]]|D|@]|E|$]]|$1|R|3|-4|5|6|7|1A|8|@]|D|@]|E|$]]]|S|$]]

NB : there's a difference between JQPL and Native query 

<pre><code>Query query = em.createQuery("SELECT COUNT(p) FROM PersonEntity p " );
</code></pre>

<code>query.getSingleResult().getClass().getCanonicalName()</code> --> java.lang.Long

<pre><code>Query query = em.createNativeQuery("SELECT COUNT(*) FROM PERSON " );
</code></pre>

<code>query.getSingleResult().getClass().getCanonicalName()</code> --> java.math.BigInteger

blocks|key|4262152|text|本机查询可以根据数据库驱动程序返回计数的不同对象；但是，所有这些对象都扩展了实现longValue()方法的java.lang.Number。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4262153|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Native queries can return different objects for a COUNT based on the database driver; however, all those objects extend java.lang.Number, which implements the longValue() method.

blocks|key|943761|text|你可以直接返回整型，而不是长整型。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|943762|return+query.getSingleResult()+!=+null+?+Integer.parseInt(query.getSingleResult().toString())+:+0;|code-block|syntax|javascript|943763|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can return directly integer, rather than a long.

<pre><code>return query.getSingleResult() != null ? Integer.parseInt(query.getSingleResult().toString()) : 0;
</code></pre>

blocks|key|945978|text|return+query.getSingleResult()+!=+null+?+Integer.parseInt(query.getSingleResult().toString())+:+0;|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|945979|unstyled|945980|第二次调用query.getSingleResult()将抛出org.hibernate.SessionException:会话已关闭！|blockquote|945981|945982|945983|为了避免org.hibernate.SessionException:会话已关闭！使用方法如下|945984|Object+obj+=+query.getSingleResult();
++++if+(obj+!=+null)+{
++++++++Integer+result+=+Integer.parseInt(obj.toString());
++++++++return+result;
++++}

++++return+Integer.valueOf(0);|945985|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|R|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|S|8|@]|9|@]|A|$]]|$1|I|3|-4|5|E|7|T|8|@]|9|@]|A|$]]|$1|J|3|-4|5|E|7|U|8|@]|9|@]|A|$]]|$1|K|3|L|5|E|7|V|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|W|8|@]|9|@]|A|$B|C]]|$1|O|3|-4|5|E|7|X|8|@]|9|@]|A|$]]]|P|$]]

<pre><code>return query.getSingleResult() != null ? Integer.parseInt(query.getSingleResult().toString()) : 0;
</code></pre>

<blockquote>
 Second call query.getSingleResult() will throw
 org.hibernate.SessionException: Session is closed!
</blockquote>

To avoid the org.hibernate.SessionException: Session is closed!
 use as below

<pre><code>Object obj = query.getSingleResult();
 if (obj != null) {
 Integer result = Integer.parseInt(obj.toString());
 return result;
 }

 return Integer.valueOf(0);
</code></pre>

What does <code>EntityManager.getSingleResult()</code> return for a COUNT query?

So.. what is the precise runtime type of foo?

<pre><code>Object foo = em.createQuery("SELECT COUNT(t) FROM com.company.Thing t WHERE prop = :param")
 .setParameter("param", value).getSingleResult();
</code></pre>

What does JPA EntityManager.getSingleResult() return for a COUNT query?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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对于计数查询，EntityManager.getSingleResult()返回什么？所以..。foo的确切运行时类型是什么？Object foo = em.createQuery("SELECT COUNT(t) FROM com.company.Thing t WHERE prop = :param")      ...

问JPA EntityManager.getSingleResult()对于计数查询返回什么？
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问JPA EntityManager.getSingleResult()对于计数查询返回什么？EN