BDL to JSON serialization options to allow nulls

In this example, the str variable is not set with a value and is therefore NULL when passed in the call to json.Serializer.variableToJSON(str, writer) and an error is raised.

IMPORT JSON

CONSTANT TNAME = "one_value_withoutNull()"
DEFINE 
    writer json.JSONWriter,
    t TEXT,
    str STRING

MAIN
    LOCATE t in MEMORY
    DISPLAY "\nSTART ", TNAME

    TRY
        LET writer = json.JSONWriter.Create()
        CALL writer.setOutputCharset("UTF-8")
        CALL writer.writeToText(t)
        CALL writer.startJSON()
        CALL json.Serializer.variableToJSON(str, writer)
        CALL writer.endJSON()
        CALL writer.close()
        DISPLAY "Should raise a serialization error"
        DISPLAY "json: ", t
        EXIT PROGRAM 1
    CATCH
        DISPLAY status || ": " || sqlca.sqlerrm
        DISPLAY "END " || TNAME || " ok"
    END TRY
END MAIN

error-15807 is raised and the following output is returned because "str" is NULL:

START one_value_withoutNull()
-15807: Primitive value cannot be serialized to 'null'
END one_value_withoutNull() ok

To avoid serialization errors, call json.Serializer.setOption("serializeNullAsDefault", 1) to allow null values, even when a JSONRequired constraint is set on the record. This is demonstrated in the following example. Note that you must reset the serializeNullAsDefault option to its default setting at the end of the program.

IMPORT JSON

CONSTANT TNAME = "object_withOption()"

DEFINE rec RECORD
    a STRING ATTRIBUTE(JSONRequired),
    b INTEGER
END RECORD
DEFINE 
    writer json.JSONWriter,
    t TEXT
MAIN
    LOCATE t in MEMORY
    DISPLAY "\nSTART ", TNAME

    TRY
        LET writer = json.JSONWriter.Create()
        CALL writer.setOutputCharset("UTF-8")
        CALL writer.writeToText(t)
        CALL writer.startJSON()
        CALL json.Serializer.setOption("serializeNullAsDefault",1)
        CALL json.Serializer.variableToJSON(rec, writer)
        CALL writer.endJSON()
        CALL writer.close()
        DISPLAY "json: ", t
    CATCH
        DISPLAY status || ": " || sqlca.sqlerrm
        EXIT PROGRAM 1
    END TRY

    DISPLAY "END " || TNAME || " ok"

    # reset serializeNullAsDefault to default
    CALL json.Serializer.setOption("serializeNullAsDefault",0)

END MAIN

START object_withOption()
json: {"a":null,"b":0}
END object_withOption() ok

By default, Genero Web Services BDL to JSON serialization will raise errors if NULL values are sent in an array as in this example:

IMPORT JSON

CONSTANT TNAME = "array_withoutNull()"
DEFINE arr DYNAMIC ARRAY OF STRING
DEFINE 
    writer json.JSONWriter,
    t TEXT

MAIN
    LOCATE t in MEMORY
    DISPLAY "\nSTART ", TNAME

    LET arr[1] = "foo"
    LET arr[2] = NULL

    TRY
        LET writer = json.JSONWriter.Create()
        CALL writer.setOutputCharset("UTF-8")
        CALL writer.writeToText(t)
        CALL writer.startJSON()
        CALL json.Serializer.variableToJSON(arr, writer)
        CALL writer.endJSON()
        CALL writer.close()
        DISPLAY "Should generate serialization error"
        DISPLAY "json: ", t
        EXIT PROGRAM 1
    CATCH
        DISPLAY status || ": " || sqlca.sqlerrm
        DISPLAY "END " || TNAME || " ok"
    END TRY
END MAIN

error-15807 is raised and the following output is returned because "arr[2]" is NULL:

START array_withoutNull()
-15807: Array cannot serialize 'null' elements. It requires json_null="null"
END array_withoutNull() ok

To prevent serialization errors in arrays, you should call json.Serializer.setOption("serializeNullAsDefault", 1) before writing to the array. This will allow null values. Note that you must reset the serializeNullAsDefault option to its default setting at the end of the program.

IMPORT JSON

CONSTANT TNAME = "array_withOption()"
DEFINE arr DYNAMIC ARRAY OF STRING
DEFINE 
    writer json.JSONWriter,
    t TEXT

MAIN
    LOCATE t in MEMORY
    DISPLAY "\nSTART ", TNAME

    LET arr[1] = "foo"
    LET arr[2] = NULL

    TRY
        LET writer = json.JSONWriter.Create()
        CALL writer.setOutputCharset("UTF-8")
        CALL writer.writeToText(t)
        CALL writer.startJSON()
        CALL json.Serializer.setOption("serializeNullAsDefault",1)
        CALL json.Serializer.variableToJSON(arr, writer)
        CALL writer.endJSON()
        CALL writer.close()
        DISPLAY "json: ", t
    CATCH
        DISPLAY status || ": " || sqlca.sqlerrm
        EXIT PROGRAM 1
    END TRY

    DISPLAY "END " || TNAME || " ok"
    # reset serializeNullAsDefault to default
    CALL json.Serializer.setOption("serializeNullAsDefault",0)
END MAIN

START array_withOption()
json: ["foo",null]
END array_withOption() ok

Alternatively, it is recommended that you define BDL variables with the attributes value json_null="null" to allow JSON serialization of null values.

DEFINE str STRING ATTRIBUTE(json_null="null")

You can define an array with the json_null="null" attribute to handle a null index or an attempt to serialize it without elements. For examples, go to Using the json_null="null" attribute.