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.

Objective-CSwift

- (void)describeWithTableName:(NSString * _Nonnull)tableName responseHandler:^(NSArray<ObjectProperty *> * _Nonnull)responseHandler errorHandler:^(Fault * _Nonnull)errorHandler;

func describe(tableName: String, responseHandler: (([ObjectProperty]) -> Void)! errorHandler: ((Fault) -> Void)!)

where:

Argument	Description
tableName	name of a data table to get the schema for.
responseHandler	a block (closure) to handle successful result of an asynchronous call.
errorHandler	a block (closure) to handle fault result of an asynchronous call.

Return value

The API returns the array of the ObjectProperty objects. The ObjectProperty protocol has the following properties:

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.
identity	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	A boolean value defining whether a property is optional or required for the requests which save the initial object or update an existing one.
type: DataTypeEnum	defines the column type.

Example

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

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

Objective-CSwift

[Backendless.shared.data describeWithTableName:@"Person" responseHandler:^(NSArray<ObjectProperty *> *properties) {
    for (ObjectProperty *property in properties) {
        NSLog(@"property name - %@", property.name);
        NSLog(@"  is property required - %s", property.required ? "true" : "false");
        NSLog(@"  property data type - %@", [property getTypeName]);
        NSLog(@"  default value - %@", property.defaultValue);
        NSLog(@"  is property primary key - %s", property.isPrimaryKey ? "true" : "false");
    }
} errorHandler:^(Fault *fault) {
    NSLog(@"Error: %@", fault.message);
}];

Backendless.shared.data.describe(tableName: "Person", responseHandler: { properties in
    for property in properties {
        print("property name - \(property.name)")
        print("  is property required - \(property.required)")
        print("  property data type - \(property.getTypeName())")
        print("  default value - \(property.defaultValue ?? NSNull())")
        print("  is property primary key - \(property.isPrimaryKey)")
    }
}, errorHandler: { fault in
    print("Error: \(fault.message ?? "")")
})

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.