Data type conversion

In high-level RESTful Web services the GWS can refine data types using JSON schema restriction keywords in the schema for types.

The OpenAPI specification defines data types for basic types, such as string, date, and number. These generally correspond to Genero BDL primitive data types.

When you need to restrict a data type (for example, to match data constraints defined on a database), the GWS can refine data types by applying JSON attribute keywords to the type specification in the schema it generates. The following sections describe how the GWS refines data types for VARCHAR, DATE/DATETIME, and DECIMAL(P,S).

VARCHAR(N)

OpenAPI defines variable-length character string data as a string. For a string type to define a VARCHAR(N) of length N, the GWS can restrict its size by using the maxLength keyword.

schema	
type           "string"
maxLength	10

fglrestful generates the data type in the client stub, mapping it to a Genero BDL VARCHAR(10) type.

DATE/DATETIME

OpenAPI defines a date type as a string. The format keyword can give this as a full date (2021-07-15), or as a date-time (2021-07-15T16:39:28Z).

As a DATE

schema	
type         "string"
format       "date"

fglrestful generates the data type in the client stub, mapping it to a Genero BDL DATE type.

As a DATETIME

schema	
type         "string"
format       "date-time"

fglrestful generates the data type in the client stub, mapping it to a Genero BDL DATETIME YEAR TO SECOND type.

By default fglrestful generates DATETIME YEAR TO SECOND. You can configure how the GWS refines the fraction part of a DATETIME type at the command level. For example, to generate DATETIME YEAR TO FRACTION(3), you can set the option --datetime-fraction=3 in the fglrestful tool command.

DECIMAL(p,s)

OpenAPI defines a fixed point decimal type as a number. For a number type to represent a fixed point decimal with precision and scale (a Genero BDL DECIMAL(p,s)), the GWS defines it with several JSON schema restriction keywords:

schema	
type	           "number"
multipleOf	      0.01
minimum	        -1000
exclusiveMinimum	true
maximum	         1000
exclusiveMaximum	true

With this example, fglrestful does the conversion for the number type schema definition as follows:

The precision (p) is calculated from the maximum and minimum values. The maximum is calculated by subtracting the multipleOf value from the maximum:
```
Maximum = 1000 - 0.01 = 999.99
```
The minimum is calculate by adding the multipleOf to the minimum:
```
Minimum = -1000 + 0.01 = -999.99
```
If the keywords exclusiveMinimum and exclusiveMaximum are set to true, the corresponding boundary is excluded. In the example, the minimum value (-1000) and the maximum (1000) are excluded.
To calculate the scale (s), fglrestful does a conversion based on the value of the multipleOf attribute. multipleOf can have two values:
- multipleOf = 0.01 is converted to DECIMAL(p,2), meaning the number of size p has two decimal places.
- multipleOf = 1 is converted to DECIMAL(p,0), meaning the number of size p has no decimal place.
- If there is no multipleOf, the number is converted to DECIMAL(p), meaning it can be any number of size p with or without decimals. There is no fixed decimal place.

In this example, fglrestful generates the data type in the client stub, mapping it to a Genero BDL DECIMAL(5,2) type. The fraction is written as DECIMAL(5,2) because five digits are needed for the precision and the scale, for example 999.99.