Thursday, 1 August 2013

OrientDB: Using Schemas with Graphs, Part 1

OrientDB is a Graph Database "on steroids" because it supports concepts taken from both the Document Database and Object-Oriented worlds.

Take a look at this use case:  Creating a graph to map the relationships between Person and Cars.  We're going to use the just-released OrientDB version 1.5.  

Let's open a shell (or command prompt in Windows) and launch the OrientDB Console (use console.bat on Windows):

> ./

Now we're going to use the console to create a brand new local database:

orientdb> create database plocal:../databases/cars admin admin plocal graph

Ok, now let's create the first graph schema with "Person" and "Car" as 2 new Vertex types and "Owns" as an Edge type:

orientdb> create class Person extends V
orientdb> create class Car extends V
orientdb> create class Owns extends E

And let's go populate the database with the first Graph elements:

orientdb> create vertex Person set name = 'Luca'

Created vertex 'Person#11:0{name:Luca} v1' in 0,012000 sec(s).

orientdb> create vertex Car set name = 'Ferrari Modena'

Created vertex 'Car#12:0{name:Ferrari Modena} v1' in 0,001000 sec(s).

orientdb> create edge Owns from (select from Person) to (select from Car)

Created edge '[e[#11:0->#12:0][#11:0-Owns->#12:0]]' in 0,005000 sec(s).

Ok, now we can traverse vertices. For example, what is Luca's car? Traverse from Luca vertex to the outgoing vertices following the "Owns" relationships:

orientdb> select name from ( select expand( out('Owns') ) from Person where name = 'Luca' )

#   |@RID |name
0   |#-2:1|Ferrari Modena

Now we have the location of Person and we need another Vertex type called "Country" to connect to the person with a new "Lives" Edge type:

orientdb> create class Country extends V
orientdb> create class Lives extends E

orientdb> create vertex Country set name = 'UK'

Created vertex 'Country#14:0{name:UK} v1' in 0,004000 sec(s).

Next, let's associate Luca to the UK Country:

orientdb> create edge Lives from (select from Person) to (select from Country)

Created edge '[e[#11:0->#14:0][#11:0-Lives->#14:0]]' in 0,006000 sec(s).

So far so good.  Our graph has been extended. 
Now, try to search the country where there are "Ferrari" cars in our database.

orientdb> select name from ( select expand( in('Owns').out('Lives') ) from Car where name like '%Ferrari%' )

#   |@RID |name
0   |#-2:1|UK

Setting constraints on Edges

Now we've modeled our graph using a schema without any constraints. But it would be useful to require an Owns relationship to exist only between the Person and Car vertices. So, let's create these constraints:

orientdb> create property Owns.out LINK Person
orientdb> create property LINK Car

The MANDATORY setting against a property prevents OrientDB from using a lightweight edge (no physical document is created).  Be sure to pay attention and not put spaces between MANDATORY=true.

orientdb> alter property Owns.out MANDATORY=true;
orientdb> alter property MANDATORY=true;

If we want to prohibit a Person vertex from having 2 edges against the same Car vertex, we have to define a UNIQUE index against out and in properties.

orientdb> create index UniqueOwns on Owns(out,in) unique

Created index successfully with 0 entries in 0,023000 sec(s).

Unfortunately, the index tells us 0 entries are indexed. Why?  We have already created the Owns relationships between "Luca" and "Ferrari Modena."  In that case, OrientDB had already created a lightweight edge before we set the rule to force creation documents for Owns instances. So, you need to drop and recreate the edge.

orientdb> delete edge from #11:0 to #12:0
orientdb> create edge Owns from (select from Person) to (select from Car)

Now check that the record has been created.

orientdb> select from Owns

#   |@RID |out  |in
0   |#13:0|#11:0|#12:0


So far so good.  The constraints works.  Now try to create a "Owns" edge between Luca and UK (Country vertex):

orientdb> create edge Owns from (select from Person) to (select from Country)

Error: com.orientechnologies.orient.core.exception.OCommandExecutionException: Error on execution of command: sql.create edge Owns from (select from Person) to (sel...
Error: com.orientechnologies.orient.core.exception.OValidationException: The field '' has been declared as LINK of type 'Car' but the value is the document #14:0 of class 'Country'

Now we have a typed graph with constraints. 

The next part will cover how to use polymorphism feature in the graph.

Luca Garulli, CEO

Orient Technologies, the Company behind OrientDB

1 comment:

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