Retrieving Schema Definition

Backendless provides API for data table schema introspection. The API returns information about table's columns and their data types, whether a value for a column is required or if there is a default value.

Non-Blocking API

Backendless.Data.Describe( string tableName, AsyncCallback<List<ObjectProperty>> callback )

Blocking API

List<ObjectProperty> Backendless.Data.Describe( string tableName )

where:

Argument	Description
tableName	name of the table to get the schema definition for.

Return value

Method returns a collection of the ObjectProperty objects. The ObjectProperty class includes the following properties:

Argument	Description
autoLoad:boolean	applies only to relations. If true, the property is set to auto-load related data for the data retrieval queries.
CustomRegex:String	a regular expression assigned to the column as a validator. The validator applies when a new object is saved in the table or an existing one is updated.
DefaultValue:Object	a default value assigned to any object saved/updated in the table where the column does not have a value.
PrimaryKey:bool	true if the column is or is a part of a primary key.
Name:String	contains the name of a property.
RelatedTable:String	contains the name of the related table(s).
IsRequired:boolean	defines whether a property is optional or required for the requests which save the initial object or update an existing one.
Type:DateTypeEnum	defines the column type.

Example

Suppose the Person table has the following schema - there are two data columns, age and name.

The following code retrieves the schema definition for the Person table:

List<ObjectProperty> properties = Backendless.Persistence.Describe( "Person" ); 

foreach( ObjectProperty property in properties ) 
{ 
  System.Console.WriteLine( "property name - " + propDef.Name );
  System.Console.WriteLine( "\tis property required - " + propDef.IsRequired );
  System.Console.WriteLine( "\tproperty data type - " + propDef.Type );
  System.Console.WriteLine( "\tdefault value - " + propDef.DefaultValue );
  System.Console.WriteLine( "\tis property identity - " + propDef.PrimaryKey );
  System.Console.WriteLine( "=====================================" ); 
}

The code produces the following output:

property name - objectId  
   is property required - false   
   property data type - STRING_ID  
   default value - null  
   is property primary key - true  
property name - age   
   is property required - false   
   property data type - INT   
   default value - null   
   is property primary key - false   
property name - updated   
   is property required - false   
   property data type - DATETIME   
   default value - null   
   is property primary key - false   
property name - name   
   is property required - false   
   property data type - STRING   
   default value - null   
   is property primary key - false   
property name - created   
   is property required - false   
   property data type - DATETIME   
   default value - null   
   is property primary key - false   
property name - ownerId   
   is property required - false  
   property data type - STRING   
   default value - null   
   is property primary key - false