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 )

where:

Argument	Description
tableName	name of the table to get the schema definition for.
callback	a responder with references to the methods called back upon successful invocation or an error.

Blocking API

public List<ObjectProperty> Backendless.Persistence.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 instances. The ObjectProperty class includes the following Java bean properties:

Argument	Description
boolean autoLoad	applies only to relations. If true, the property is set to auto-load related data for the data retrieval queries.
String customRegex	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.
Object defaultValue	a default value assigned to any object saved/updated in the table where the column does not have a value.
boolean isPrimaryKey	true if the column is or is a part of a primary key.
String name	contains the name of a property Consider the
String relatedTable	contains the name of the related table(s)
boolean required	defines whether a property is optional or required for the requests which save the initial object or update an existing one.
String type	defines the property 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:

Backendless.Persistence.describe( "Person", new AsyncCallback<List<ObjectProperty>>() 
   { 
     public void handleResponse( List<ObjectProperty> tableProperties ) 
     {     
       Iterator<ObjectProperty> iterator = tableProperties;

       while( iterator.hasMore() )
       {
         ObjectProperty propDef = iterator.next();
         Log.i( "MYAPP", "property name - " + propDef.getName() );
         Log.i( "MYAPP", "\tis property required - " + propDef.isRequired() );
         Log.i( "MYAPP", "\tproperty data type - " + propDef.getType() );
         Log.i( "MYAPP", "\tdefault value - " + propDef.getDefaultValue() );
         Log.i( "MYAPP", "\tis property identity - " + propDef.getPrimaryKey() );
       }
     } 

     public void handleFault( BackendlessFault backendlessFault ) 
     {              
     } 
} );

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

Codeless Reference

where:

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

Returns a list containing objects each with the following structure:

{  
autoLoad: true or false,  
customRegex: value,  
defaultValue: null or value,  
isPrimaryKey: true or false,  
name: value,  
relatedTable: null or table name,  
required: true or false,  
type: data type  
}

where:

Argument	Description
autoLoad	Applies only to relations. If true, the property is set to auto-load related data for the data retrieval queries.
customRegex	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	A default value assigned to any object saved/updated in the table where the column does not have a value.
isPrimaryKey	true if the column is or is a part of a primary key.
name	Contains the name of a property.
relatedTable	Contains the name of the related table. This is applicable only to relation columns.
required	Defines whether a property is optional or required for the requests which save the initial object or update an existing one.
type	Defines the column type.

The schema of the data table presented below has three custom columns: name, position, and phoneNumber.

The operation below retrieves the schema of the employees data table.

The result of this operation will look as shown below after the Codeless logic runs. As you can see,  the operation returns a list of objects containing detailed information about each column.