It's easier to introduce OrientDB's basic concepts by outlining the Document Database API. It is more similar to Relational DBMS concepts and therefore a little more natural to follow for many developers. These basic concepts are shared between all of OrientDB's APIs: Document, Object, and Graph.
As with the relational DBMS, OrientDB has the concept of records as an element of storage. There are different types of records, but for the next examples we will always use the document type. A document is composed of attributes and can belong to one class. Going forward we will also refer to the attributes with the terms "fields" and "properties".
The concept of class is well known to those who program using object-oriented languages. Classes are also used in OrientDB as a type of data model according to certain rules. To learn more about Classes in general take a look at Wikipedia.
To list all the configured classes, type the classes command in the console:
orientdb> classes
CLASSES:
----------------------------------------------+---------------------+-----------+
NAME | CLUSTERS | RECORDS |
----------------------------------------------+---------------------+-----------+
AbstractPerson | -1 | 0 |
Account | 11 | 1126 |
Actor | 91 | 3 |
Address | 19 | 166 |
Animal | 17 | 0 |
.... | .... | .... |
Whiz | 14 | 1001 |
----------------------------------------------+---------------------+-----------+
TOTAL 22775 |
--------------------------------------------------------------------------------+
To create a new class, use the create class command:
orientdb> create class Student
Class created successfully. Total classes in database now: 92
OrientDB allows you to work in a schema-less mode, without defining properties. However, properties are mandatory if you define indexes or constraints. To create a new property use the create property command. Here is an example of creating three properties against the Student class:
orientdb> create property Student.name string
Property created successfully with id=1
orientdb> create property Student.surname string
Property created successfully with id=2
orientdb> create property Student.birthDate date
Property created successfully with id=3
To display the class Student, use the info class command:
orientdb> info class Student
Class................: Student
Default cluster......: student (id=96)
Supported cluster ids: [96]
Properties:
-------------------------------+-------------+-------------------------------+-----------+----------+----------+-----------+-----------+
NAME | TYPE | LINKED TYPE/CLASS | MANDATORY | READONLY | NOT NULL | MIN | MAX |
-------------------------------+-------------+-------------------------------+-----------+----------+----------+-----------+-----------+
birthDate | DATE | null | false | false | false | | |
name | STRING | null | false | false | false | | |
surname | STRING | null | false | false | false | | |
-------------------------------+-------------+-------------------------------+-----------+----------+----------+-----------+-----------+
To add a constraint, use the alter class command. For example, let's specify that the name field should be at least 3 characters:
orientdb> alter property Student.name min 3
Property updated successfully
To see all the records in a class, use the browse class command:
> browse class OUser
In this case we are listing all of the users of the database. This is not particularly secure. You should further deepen the OrientDB security system, but for now OUser is a class like any other. For each query the console always shows us the number of the records in the result set and the record's ID.
---+---------+--------------------+--------------------+--------------------+--------------------
#| RID |name |password |status |roles
---+---------+--------------------+--------------------+--------------------+--------------------
0| #5:0|admin |{SHA-256}8C6976E5B5410415BDE908BD4DEE15DFB167A9C873FC4BB8A81F6F2AB448A918|ACTIVE |[1]
1| #5:1|reader |{SHA-256}3D0941964AA3EBDCB00CCEF58B1BB399F9F898465E9886D5AEC7F31090A0FB30|ACTIVE |[1]
2| #5:2|writer |{SHA-256}B93006774CBDD4B299389A03AC3D88C3A76B460D538795BC12718011A909FBA5|ACTIVE |[1]
---+---------+--------------------+--------------------+--------------------+--------------------
The first column is a number used as an identifier to display the record's detail. To show the first record in detail, it is necessary to use the display record command with the number of the record, in this case 0:
orientdb> display record 0
--------------------------------------------------
ODocument - Class: OUser id: #5:0 v.0
--------------------------------------------------
name : admin
password : {SHA-256}8C6976E5B5410415BDE908BD4DEE15DFB167A9C873FC4BB8A81F6F2AB448A918
status : ACTIVE
roles : [#4:0=#4:0]