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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.

Backendless.Data.describe( tableName )
 .then( function( schemaProps ) {
  })
 .catch( function( error ) {
  });

where:

Argument                Description
tableName name of a table for which to retrieve schema definition.

Return value:

Returns an array of object's properties. Each object in the array describes a column in the specified table using the structure below:

{
  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(s).
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 property type.

Example

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

person-schema.zoom70

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

Backendless.Data.describe( "Person" )
 .then( function( schemaArray ) {
    for( var i in schemaArray )
    {
      console.log( "property name - " + schemaArray[ i ].name );
      console.log( "\tis property required - " + schemaArray[ i ].required );
      console.log( "\tproperty data type - " + schemaArray[ i ].type );
      console.log( "\tdefault value - " + schemaArray[ i ].defaultValue );
      console.log( "\tis property primary key - " + schemaArray[ i ].identity );
    }   
  })
 .catch( function( error ) {
 });

The code produces the following output: 
property name - objectId  
   is property required - false   
   property data type - STRING_ID  
   default value - null  
   is property identity - undefined  
property name - age   
   is property required - false   
   property data type - INT   
   default value - null   
   is property identity - undefined   
property name - updated   
   is property required - false   
   property data type - DATETIME   
   default value - null   
   is property identity - undefined   
property name - name   
   is property required - false   
   property data type - STRING   
   default value - null   
   is property identity - undefined   
property name - created   
   is property required - false   
   property data type - DATETIME   
   default value - null   
   is property identity - undefined   
property name - ownerId   
   is property required - false  
   property data type - STRING   
   default value - null   
   is property identity - undefined