blocks|key|4334009|text|可能不是您想要听到的，但是AFAIK没有办法有条件地包含注释。另一种方法是在@MappedSuperclass中包含通用功能，并根据环境在构建时适当地注入具体实例。就像这样：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4334010|@MappedSuperclass
abstract+class+AbstractClientJpa+{
++++var+surrogateKey:+Int+++//+abstract
++++var+code:+String+=+_
++++var+name:+String+=+_
}|code-block|syntax|javascript|4334011|..。|4334012|@Entity
@Table(name+=+"clients")
class+HanaClientJpa+extends+AbstractClientJpa+{
++++@Id
++++@GeneratedValue(strategy+=+GenerationType.SEQUENCE,+generator+=+"generator")
++++@SequenceGenerator(name="generator",+sequenceName+=+"cliSeq",+allocationSize+=+1)++++
++++var+surrogateKey:+Int+=+_
}|4334013|4334014|@Entity
@Table(name+=+"clients")
class+MySQLClientJpa+extends+AbstractClientJpa+{
++++@Id
++++@GeneratedValue(strategy+=+GenerationType.IDENTITY)
++++var+surrogateKey:+Int+=+_
}|4334015|entityMap^0|12|H|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|W|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|X|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|O|3|L|5|6|7|Z|8|@]|D|@]|E|$]]|$1|P|3|Q|5|H|7|10|8|@]|D|@]|E|$I|J]]|$1|R|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|S|$]]

Probably not what you want to hear but AFAIK there's no way to conditionally include annotations. An alternative would be to include the common functionality in a <code>@MappedSuperclass</code> and inject the concrete instance as appropriate at build time depending on the environment. Something like this:-

<pre><code>@MappedSuperclass
abstract class AbstractClientJpa {
 var surrogateKey: Int // abstract
 var code: String = _
 var name: String = _
}
</code></pre>

...

<pre><code>@Entity
@Table(name = "clients")
class HanaClientJpa extends AbstractClientJpa {
 @Id
 @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "generator")
 @SequenceGenerator(name="generator", sequenceName = "cliSeq", allocationSize = 1) 
 var surrogateKey: Int = _
}
</code></pre>

...

<pre><code>@Entity
@Table(name = "clients")
class MySQLClientJpa extends AbstractClientJpa {
 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 var surrogateKey: Int = _
}
</code></pre>

blocks|key|4334062|text|我认为这样做的方法是提供一个自定义的IdGeneratorStrategyInterpreter并使用MetadataBuilder.applyIdGenerationTypeInterpreter注册它。在自定义IdGeneratorStrategyInterpreter中，如果您知道代码是针对MySql运行的，则可以覆盖determineGeneratorName为GenerationType.SEQUENCE返回"identity"常量，在所有其他情况下返回null，以便让FallbackInterpreter执行其默认工作(字符串"identity"也来自FallbackInterpreter.determineGeneratorName实现)。你不能在其他方法中做任何事情，让FallbackInterpreter来做它通常的工作。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4334063|另外，请注意，Hibernate的默认SequenceStyleGenerator实际上知道DB不支持“序列”(通过Dialect.supportsSequences公开)，并且能够使用附加表模拟类似的行为。对于您的场景，这可能是可以的，也可能不是。|4334064|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.jboss.org/hibernate/orm/5.2/javadocs/org/hibernate/boot/model/IdGeneratorStrategyInterpreter.html|1|https://docs.jboss.org/hibernate/orm/5.2/javadocs/org/hibernate/boot/MetadataBuilder.html#applyIdGenerationTypeInterpreter-org.hibernate.boot.model.IdGeneratorStrategyInterpreter-|2|https://github.com/hibernate/hibernate-orm/blob/d5d3b080f94ca2f498bada7747bbda1e0e3160a2/hibernate-core/src/main/java/org/hibernate/boot/internal/IdGeneratorInterpreterImpl.java#L211-L238|3|https://docs.jboss.org/hibernate/orm/5.0/javadocs/org/hibernate/id/enhanced/SequenceStyleGenerator.html|4|https://docs.jboss.org/hibernate/orm/5.0/javadocs/org/hibernate/dialect/Dialect.html#supportsSequences--^0|I|U|1F|1C|2Z|U|4J|M|56|N|5V|A|6I|4|6Q|J|7K|A|7X|16|9N|J|I|U|0|1F|1C|1|7X|16|2|0|J|M|1M|P|J|M|3|1M|P|4|0^^$0|@$1|2|3|4|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]|$9|14|A|15|B|C]|$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]]|D|@$9|1K|A|1L|1|1M]|$9|1N|A|1O|1|1P]|$9|1Q|A|1R|1|1S]]|E|$]]|$1|F|3|G|5|6|7|1T|8|@$9|1U|A|1V|B|C]|$9|1W|A|1X|B|C]]|D|@$9|1Y|A|1Z|1|20]|$9|21|A|22|1|23]]|E|$]]|$1|H|3|-4|5|6|7|24|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]|P|$5|K|L|M|E|$N|Q]]|R|$5|K|L|M|E|$N|S]]|T|$5|K|L|M|E|$N|U]]|V|$5|K|L|M|E|$N|W]]]]

I think the way to do it is to provide a custom <a href="https://docs.jboss.org/hibernate/orm/5.2/javadocs/org/hibernate/boot/model/IdGeneratorStrategyInterpreter.html" rel="nofollow noreferrer"><code>IdGeneratorStrategyInterpreter</code></a> and register it using <a href="https://docs.jboss.org/hibernate/orm/5.2/javadocs/org/hibernate/boot/MetadataBuilder.html#applyIdGenerationTypeInterpreter-org.hibernate.boot.model.IdGeneratorStrategyInterpreter-" rel="nofollow noreferrer"><code>MetadataBuilder.applyIdGenerationTypeInterpreter</code></a>. In your custom <code>IdGeneratorStrategyInterpreter</code> you can override <code>determineGeneratorName</code> to return <code>"identity"</code> constant for <code>GenerationType.SEQUENCE</code> if you know that the code is run against MySql and return <code>null</code> in all other cases to let the <code>FallbackInterpreter</code> do its default job (the string <code>"identity"</code> also comes from <a href="https://github.com/hibernate/hibernate-orm/blob/d5d3b080f94ca2f498bada7747bbda1e0e3160a2/hibernate-core/src/main/java/org/hibernate/boot/internal/IdGeneratorInterpreterImpl.java#L211-L238" rel="nofollow noreferrer"><code>FallbackInterpreter.determineGeneratorName</code></a> implementation). And you can do nothing in other methods and let the <code>FallbackInterpreter</code> do it's usual job.

P.S. Please also note that Hibernate's default <a href="https://docs.jboss.org/hibernate/orm/5.0/javadocs/org/hibernate/id/enhanced/SequenceStyleGenerator.html" rel="nofollow noreferrer"><code>SequenceStyleGenerator</code></a> is actually aware of DBs not supporting "sequences" (exposed via <a href="https://docs.jboss.org/hibernate/orm/5.0/javadocs/org/hibernate/dialect/Dialect.html#supportsSequences--" rel="nofollow noreferrer"><code>Dialect.supportsSequences</code></a>) and is able to emulate similar behavior using additional table. This might or might not be OK for your scenario.

blocks|key|4334139|text|这个答案试图实现Eugene's+suggestion+(因此，如果它有效，请归功于Eugene)。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4334140|给定@ifNotMysql宏的以下定义|style|CODE|4334141|import+scala.reflect.macros.blackbox
import+scala.language.experimental.macros
import+scala.annotation.{StaticAnnotation,+compileTimeOnly}

object+ifNotMysqlMacro+{
++val+targetIsMySql+=+sys.props.get("target-mysql").contains("true")

++def+impl(c:+blackbox.Context)(annottees:+c.Expr[Any]*):+c.Expr[Any]+=+{
++++import+c.universe._

++++def+mysqlAnnots(annotations:+Seq[c.universe.Tree]):+Seq[c.universe.Tree]+=
++++++annotations
++++++++.filterNot(_.toString.contains("SequenceGenerator"))
++++++++.filterNot(_.toString.contains("GeneratedValue"))
++++++++.:%2B(q"""new+GeneratedValue(strategy+=+GenerationType.IDENTITY)""")

++++val+result+=+annottees.map(_.tree).toList+match+{
++++++case+q"@..$annots+var+$pat:+$tpt+=+$expr"+::+Nil+=>
++++++++q"""
++++++++++++@..${if+(targetIsMySql)+mysqlAnnots(annots)+else+annots}
++++++++++++var+$pat:+$tpt+=+$expr
++++++++++"""
++++}
++++c.Expr[Any](result)
++}
}

@compileTimeOnly("enable+macro+paradise+to+expand+macro+annotations")
class+ifNotMysql+extends+StaticAnnotation+{
++def+macroTransform(annottees:+Any*):+Any+=+macro+ifNotMysqlMacro.impl
}|code-block|syntax|javascript|4334142|如果我们这样编写@ifNotMysql+@GeneratedValue(...)+@SequenceGenerator|4334143|@ifNotMysql+
@GeneratedValue(strategy+=+GenerationType.SEQUENCE,+generator+=+"generator")
@SequenceGenerator(name="generator",+sequenceName+=+"cliSeq",+allocationSize+=+1)++++
var+surrogateKey:+Int+=+_|4334144|并提供系统属性target-mysql，如下所示|4334145|sbt+-Dtarget-mysql=true+compile|4334146|则将排除@SequenceGenerator注释，并按如下方式添加@GeneratedValue(strategy+=+GenerationType.IDENTITY)|4334147|@GeneratedValue(strategy+=+GenerationType.IDENTITY)
var+surrogateKey:+Int+=+_|4334148|此实现基于scalamacros/sbt-example-paradise|4334149|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/47995473/how-to-conditionally-include-a-hibernate-annotation#answer-50614632|1|https://github.com/scalamacros/sbt-example-paradise/blob/master/macros/src/main/scala/Macros.scala^0|8|J|0|0|2|B|0|0|8|1F|0|0|7|C|0|0|4|I|X|1F|0|0|5|W|1|0^^$0|@$1|2|3|4|5|6|7|1A|8|@]|9|@$A|1B|B|1C|1|1D]]|C|$]]|$1|D|3|E|5|6|7|1E|8|@$A|1F|B|1G|F|G]]|9|@]|C|$]]|$1|H|3|I|5|J|7|1H|8|@]|9|@]|C|$K|L]]|$1|M|3|N|5|6|7|1I|8|@$A|1J|B|1K|F|G]]|9|@]|C|$]]|$1|O|3|P|5|J|7|1L|8|@]|9|@]|C|$K|L]]|$1|Q|3|R|5|6|7|1M|8|@$A|1N|B|1O|F|G]]|9|@]|C|$]]|$1|S|3|T|5|J|7|1P|8|@]|9|@]|C|$K|L]]|$1|U|3|V|5|6|7|1Q|8|@$A|1R|B|1S|F|G]|$A|1T|B|1U|F|G]]|9|@]|C|$]]|$1|W|3|X|5|J|7|1V|8|@]|9|@]|C|$K|L]]|$1|Y|3|Z|5|6|7|1W|8|@]|9|@$A|1X|B|1Y|1|1Z]]|C|$]]|$1|10|3|-4|5|6|7|20|8|@]|9|@]|C|$]]]|11|$12|$5|13|14|15|C|$16|17]]|18|$5|13|14|15|C|$16|19]]]]

This answer attempts to implement <a href="https://stackoverflow.com/questions/47995473/how-to-conditionally-include-a-hibernate-annotation#answer-50614632">Eugene's suggestion</a> (so if it works please give credit to Eugene).

Given the following definition of <code>@ifNotMysql</code> macro

<pre><code>import scala.reflect.macros.blackbox
import scala.language.experimental.macros
import scala.annotation.{StaticAnnotation, compileTimeOnly}

object ifNotMysqlMacro {
 val targetIsMySql = sys.props.get("target-mysql").contains("true")

 def impl(c: blackbox.Context)(annottees: c.Expr[Any]*): c.Expr[Any] = {
 import c.universe._

 def mysqlAnnots(annotations: Seq[c.universe.Tree]): Seq[c.universe.Tree] =
 annotations
 .filterNot(_.toString.contains("SequenceGenerator"))
 .filterNot(_.toString.contains("GeneratedValue"))
 .:+(q"""new GeneratedValue(strategy = GenerationType.IDENTITY)""")

 val result = annottees.map(_.tree).toList match {
 case q"@..$annots var $pat: $tpt = $expr" :: Nil =&gt;
 q"""
 @..${if (targetIsMySql) mysqlAnnots(annots) else annots}
 var $pat: $tpt = $expr
 """
 }
 c.Expr[Any](result)
 }
}

@compileTimeOnly("enable macro paradise to expand macro annotations")
class ifNotMysql extends StaticAnnotation {
 def macroTransform(annottees: Any*): Any = macro ifNotMysqlMacro.impl
}
</code></pre>

if we write <code>@ifNotMysql @GeneratedValue(...) @SequenceGenerator</code> like so

<pre><code>@ifNotMysql 
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "generator")
@SequenceGenerator(name="generator", sequenceName = "cliSeq", allocationSize = 1) 
var surrogateKey: Int = _
</code></pre>

and provide system property <code>target-mysql</code> like so

<pre><code>sbt -Dtarget-mysql=true compile
</code></pre>

then <code>@SequenceGenerator</code> annotation will be excluded and <code>@GeneratedValue(strategy = GenerationType.IDENTITY)</code> added like so

<pre><code>@GeneratedValue(strategy = GenerationType.IDENTITY)
var surrogateKey: Int = _
</code></pre>

This implementation is based on <a href="https://github.com/scalamacros/sbt-example-paradise/blob/master/macros/src/main/scala/Macros.scala" rel="nofollow noreferrer">scalamacros/sbt-example-paradise</a>

blocks|key|4334500|text|如果mysql中的ID是自动递增的，那么在hibernate映射中ID应该是IDENTITY|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4334501|将其替换为|4334502|@Entity
@Table(name="clients")
class+ClientJpa{
++@Id
++@GeneratedValue(strategy+=+GenerationType.IDENTITY,+generator+=+"generator")
++var+surrogateKey:+Int+=+_
++var+code:+String+=+_
++var+name:+String+=+_

+}|code-block|syntax|javascript|4334503|希望它能用..。|4334504|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

If ID in mysql is given auto-increment then in hibernate mapping ID should be IDENTITY

Replace that with

<pre><code>@Entity
@Table(name="clients")
class ClientJpa{
 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY, generator = "generator")
 var surrogateKey: Int = _
 var code: String = _
 var name: String = _

 }
</code></pre>

Hope it works....

I have the code below in Play for Scala to access a SAP Hana table with Hibernate. I need to implement the same code with MySql, but the problem is that MySql doesn't support sequences (it works with AUTO_INCREMENT columns) and the code breaks because I have to specify <code>@SequenceGenerator</code> for Hana. Is there a way to compile this code with a condition to exclude the <code>@SequenceGenerator</code> annotation, so it works for MySql and Hana at the same time?

<pre><code>@Entity
@Table(name = "clients")
class ClientJpa {

 @Id
 @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "generator")
 @SequenceGenerator(name="generator", sequenceName = "cliSeq", allocationSize = 1) 
 var surrogateKey: Int = _
 var code: String = _
 var name: String = _
}
</code></pre>

How to conditionally include a Hibernate annotation?

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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我有下面的代码，让Scala使用Hibernate访问SAP Hana表。我需要用MySql实现相同的代码，但问题是MySql不支持序列(它适用于AUTO_INCREMENT列)和代码中断，因为我必须为Hana指定@SequenceGenerator。有没有办法用一个条件来编译这段代码，以排除@SequenceGene...

问如何有条件地包含Hibernate注释？
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问如何有条件地包含Hibernate注释？EN