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Author: alien
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Khóa học miễn phí OrientDB – Create Class nhận dự án làm có lương
OrientDB – Create Class
OrientDB supports multi-model feature and provides different ways in approaching and understanding the basic concepts of a database. However, we can easily access these models from the perspective of Document database API. Like RDBMS, OrientDB also uses the Record as an element of storage but it uses the Document type. Documents are stored in the form of Key/Value pairs. We are storing fields and properties as key/value pairs which belong to a concepts class.
Class is a type of data model and the concept is drawn from the Object-oriented programming paradigm. Based on the traditional document database model, data is stored in the form of collection, while in the relational database model data it is stored in tables. OrientDB follows the Document API along with OPPS paradigm. As a concept, class in OrientDB has the closest relationship with the table in relational databases, but (unlike tables) classes can be schema-less, schema-full or mixed. Classes can inherit from other classes, creating trees of classes. Each class has its own cluster or clusters, (created by default, if none are defined).
The following statement is the basic syntax of the Create Class Command.
CREATE CLASS <class> [EXTENDS <super-class>] [CLUSTER <cluster-id>*] [CLUSTERS <total-cluster-number>] [ABSTRACT]
Following are the details about the options in the above syntax.
<class> − Defines the name of the class you want to create.
<super-class> − Defines the super-class you want to extend with this class.
<total-cluster-number> − Defines the total number of clusters used in this class. Default is 1.
ABSTARCT − Defines the class is abstract. This is optional.
Example
As discussed, class is a concept related to table. Therefore here we will create a table Account. However, while creating class we cannot define fields i.e., properties based on OOPS paradigm.
The following command is to create a class named Account.
orientdb> CREATE CLASS Account
If the above command is executed successfully, you will get the following output.
Class created successfully
You can use the following command to create a class Car which extends to class Vehicle.
orientdb> CREATE CLASS Car EXTENDS Vehicle
If the above command is executed successfully, you will get the following output.
Class created successfully
You can use the following command to create a class Person as abstract.
orientdb> CREATE CLASS Person ABSTRACT
If the above command is executed successfully, you will get the following output.
Class created successfully
Note − Without having properties, the class is useless and unable to build real object. In the further chapters, you can learn how to create properties for a particular class.
Khóa học lập trình tại Toidayhoc vừa học vừa làm dự án vừa nhận lương: Khóa học lập trình nhận lương tại trung tâm Toidayhoc
Khóa học miễn phí OrientDB – Delete Record nhận dự án làm có lương
OrientDB – Delete Record
Delete Record command is used to delete one or more records completely from the database.
The following statement is the basic syntax of the Delete command.
DELETE FROM <Class>|cluster:<cluster>|index:<index> [LOCK <default|record>] [RETURN <returning>] [WHERE <Condition>*] [LIMIT <MaxRecords>] [TIMEOUT <timeout>]
Following are the details about the options in the above syntax.
LOCK − Specifies how to lock the records between load and update. We have two options to specify Default and Record.
RETURN − Specifies an expression to return instead of the number of records.
LIMIT − Defines the maximum number of records to update.
TIMEOUT − Defines the time you want to allow the update run before it times out.
Note − Don’t use DELETE to remove Vertices or Edges because it effects the integrity of the graph.
Example
Let us consider the Customer table.
| Sr.No. | Name | Age |
|---|---|---|
| 1 | Satish | 25 |
| 2 | Krishna | 26 |
| 3 | Kiran | 29 |
| 4 | Javeed | 21 |
Try the following query to delete the record having id = 4.
orientdb {db = demo}> DELETE FROM Customer WHERE id = 4
If the above query is executed successfully, you will get the following output.
Delete 1 record(s) in 0.008000 sec(s).
To check the record of Customer table you can use the following query.
Orientdb {db = demo}> SELECT FROM Customer
If the above query is executed successfully, you will get the following output.
----+-----+--------+----+-------+---- # |@RID |@CLASS |id |name |age ----+-----+--------+----+-------+---- 0 |#11:0|Customer|1 |satish |25 1 |#11:1|Customer|2 |krishna|26 2 |#11:2|Customer|3 |kiran |29 ----+-----+--------+----+-------+----
Khóa học lập trình tại Toidayhoc vừa học vừa làm dự án vừa nhận lương: Khóa học lập trình nhận lương tại trung tâm Toidayhoc