Console - CREATE LINK

The Create Link command creates links between two or more records of type Document. This is very useful when you're importing data from a Relational database. In facts in the Relational world relationships are resolved as foreign keys.

Consider this example where the class "Post" has a relationship 1-N to "Comment":

Post 1 ---> * Comment

In a Relational database you'll have something like that:

Table Post
+----+----------------+
| Id | Title          |
+----+----------------+
| 10 | NoSQL movement |
| 20 | New OrientDB   |
+----+----------------+

Table Comment
+----+--------+--------------+
| Id | PostId | Text         |
+----+--------+--------------+
|  0 |   10   | First        |
|  1 |   10   | Second       |
| 21 |   10   | Another      |
| 41 |   20   | First again  |
| 82 |   20   | Second Again |
+----+--------+--------------+

Using OrientDB, instead, you have direct relationship as in your object model. So the navigation is from Post to Comment and not viceversa as for Relational model. For this reason you need to create a link as INVERSE.

Syntax

CREATE LINK <link-name> FROM <source-class>.<source-property> TO <destination-class>.<destination-property>

Where:

• link-name is the name of the property for the link. If not expressed will be overwritten the destination-property field
• source-class, is the source class
• source-property, is the source property
• destination-class, is the destination class
• destination-property, is the destination property

Examples

CREATE LINK comments FROM comments.!PostId To posts.Id INVERSE

To know more about other SQL commands look at SQL SQL commands.

This is a command of the Orient console. To know all the commands go to Console-Commands.