Create custom domain Constraints for validating Domain objects

This Blog is for creating the Custom Constraints Validation for Domain .

Purpose -> This type of requirements come in any situation like in our project , We use Neo4j database and Spring Data Neo4j , So unique constraints that grails Plugin provide we cannot use because SDN does not provide any type of Constraints . So we have to implement Custom Validator.

Plugin use -

compile ":constraints:0.8.0"

1. Create a groovy file in /grails-app/utils/ called *Constraint.groovy
2. Implement a validate closure
   Ex ->

   class UniqueUserConstraint {
       //static name ="uniqueName"
       static expectsParams = true
       static defaultMessageCode = "default.not.unique.message"
       def neo4jTemplate
       /*
        * This validation is for checking unique , it work in all cases  
        * for saving , update  anything  
        */
       def validate = {  val ,target->        
           Result> result = neo4jTemplate.query("match (n:"+params.domainClass+") where n."+params.propertyName+" = '"+val+"' return n", null)
           for (Map m : result) {
               for (Map.Entry e : m.entrySet()) {
                   org.neo4j.kernel.impl.core.NodeProxy node =  e.getValue();
                   Long nodeId=node.getId()
                   Long userId=target.id 
                   if(node!=0){
                       if(nodeId==userId){
                           return true
                       }
                   return  'default.not.unique.message'
                   }
               }
           
           }
           return true
       }
   }
   

   Apply the validation to a Domain class

   	
   username size: 5..55, blank: false,
   
   	uniqueUser:['domainClass':'User','propertyName':'username']

    

3. We have username as a Property in our Database , you can use this constraints anywhere in your code , just pass the correct parameter Domain class , propertyname is username , if you want to use unique constraints on email then propertName should be 'email'

For more information use this link Custom Validation