Param Usage ​

Through【By Custom nGQL】, we have known how to make the nGQL | cypher written by ourselves call and execute it into Nebula through Java. Next, in this section, we will introduce how to pass parameters to the statements.

Attention: The basic types of all parameters currently only support wrapper classes. For example, int needs to be written as Integer.

Read Parameters in nGQL | cypher ​

Named Parameters ​

The parameters are annotated by @Param. ( org.springframework.data.repository.query.Param )

Basic Types ​

• PersonDao.java

  java

  // org.springframework.data.repository.query.Param
      Person selectByName( @Param("name") String param );

• PersonDao.xml

  xml

  <select id="selectByName">
      MATCH (n: person)
      WHERE n.person.name == $name
      RETURN n
      LIMIT 1
  </select>

POJO or Map ​

• PersonDao.java

  java

  // org.springframework.data.repository.query.Param
      Person selectByName( @Param("person") Person person );

• PersonDao.xml

  xml

  <select id="selectByName">
      MATCH (n: person)
      WHERE n.person.name == $person.name
      RETURN n
      LIMIT 1
  </select>

Parameter reading supports . operator

Anonymous Parameters ​

• If there is no @Param annotation in the parameters declared in the interface, the index is used to obtain, that is: $p0、$p1、$p2、$p3 ...
• When the length of the parameter list is 1 and the type is POJO or Map, the attribute can be read directly

Basic Type ​

• PersonDao.java

  java

  Person selectByName( String name );

• PersonDao.xml

  参数由 NgBatis 替换，方式1方式 2参数由 DB 替换

  xml

  <select id="selectByName">
      MATCH (n: person)
      WHERE n.person.name == '${ name }'
      RETURN n
      LIMIT 1
  </select>

  xml

  <select id="selectByName">
      MATCH (n: person)
      WHERE n.person.name == ${ ng.valueFmt(name) } // 可以忽略类型差异
      RETURN n
      LIMIT 1
  </select>

  xml

  <select id="selectByName">
      MATCH (n: person)
      WHERE n.person.name == $name
      RETURN n
      LIMIT 1
  </select>

  xml

  <select id="selectByName">
      MATCH (n: person)
      WHERE n.person.name == $p0
      RETURN n
      LIMIT 1
  </select>

POJO or Map ​

When there is only one parameter ​

• PersonDao.java

  java

  Person selectByName( Person person );

• PersonDao.xml

  xml

  <select id="selectByName">
      MATCH (n: person)
      WHERE n.person.name == $name
      RETURN n
      LIMIT 1
  </select>

When there are two or more parameters ​

• PersonDao.java

  java

  // params = { age: 18 }
      Person selectByName( Person person, Map<String, Object> params );

• PersonDao.xml

  xml

  <select id="selectByName">
          MATCH (n: person)
          WHERE n.person.name == $p0.name
          AND n.person.age > $p1.age
          RETURN n
          LIMIT 1
      </select>

The parameter acquisition of the collection type is consistent with the basic types ​

• When anonymous, use $p0，$p1，...;
• When naming, directly use the parameter name in the annotation;
• If it is a collection of basic types, it can be directly passed in without complex processing.

• PersonDao.java

  java

  List<Person> findByIds( List<String> names );

• PersonDao.xml

  xml

  <select id="findByIds" resultType="your.domain.Person">
          MATCH (n: person)
          WHERE id(n) in $p0
          RETURN n
      </select>

Conclusion ​

This completes the general introduction of parameter acquisition. If you have requirements for condition control and traversal after obtaining parameters, please move to【Param Condition Control】、【Param Loop】