Neo4j Create Constraint

The neo4j constraint helps user to nor enter in wrong kind of data. When the constraint is applied and the user by mistake entering the wrong kind of data then it will show an error message. In the neo4j there are two kind of constraint one is uniqueness constraints and other one is property existence constraints. Below is the example of both the constraint with the example: Suppose there is already below database is exist.

CREATE(CPP:Language{id:001, Designer: "Bjarne Stroustrup", YOE: 1985}) 
CREATE(C:Language {id:002, Designer: "Dennis Ritchie", YOE: 1972}) 
CREATE(Python:Language {id:003, Designer: "Guido van Rossum ", YOE: 1990}) 
CREATE(Java:Language {id:004, Designer: "James Gosling", YOE: 1995}) 
CREATE(CSharp:Language {id:005, Designer: "Microsoft", YOE: 2000})
RETURN CPP, C, Python, Java, CSharp 

Output: 👁 Image

Uniqueness Constraints: This Constraint contain a unique value, in his constraint two same lebel can't share a same id.
• Query:

  CREATE CONSTRAINT ON(l:Language) ASSERT l.id IS UNIQUE

  Output: 👁 Image
  
• View the Constraint:

  :schema

  Output: 👁 Image
  
• Test the Constraint: Here we will try to add another node into that database with a redundant id value(004). Query:

  CREATE(Neo4j:Language {id:004, Designer: "Neo4j", YOE: 2012})

  Output: 👁 Image
  

Property Existence Constraints: Property existence constraints is used to ensure all nodes with a certain label have a certain property. For example, you could specify that all nodes labelled with Language must contain a id property.
• Query:

  CREATE CONSTRAINT ON (label) ASSERT exists(node)

Note: Property existence constraints are only available in the Neo4j Enterprise Edition.