How to Pass an Array of Object Type
To Static Function of That Type

Solution shorter than the title

Array of an Object Type Argument in a Function of That Object Type

Interesting question regarding Object Types was asked not a long ago on StackOverflow:

How to Pass a Nested Table of Object Type to a Function of That Object Type?

What author was trying to accomplish was to declare a static function in an object type which would take as a parameter an array of objects of the object type in which it was declared.

Is that even possible? (dramatic pause)

First Try

Let’s check firstly if we can define a non-array parameter of the same object type:

CREATE OR REPLACE 
TYPE my_object AS OBJECT (
  some_number NUMBER,
  STATIC FUNCTION static_test_function(
                     p_my_object IN my_object) RETURN NUMBER
);
/
> TYPE MY_OBJECT compiled

Alright, no errors – now let’s create a nested table type of my_object type:

CREATE TYPE my_objects_tab_t IS TABLE OF my_object;
/
TYPE MY_OBJECTS_TAB_T compiled

So far, so good. Next, let’s alter declaration of my_object‘s static function to take my_objects_tab_t as an argument:

CREATE OR REPLACE 
TYPE my_object AS OBJECT (
  some_number NUMBER,
  STATIC FUNCTION static_test_function(
           p_my_objects_tab IN my_objects_tab_t) RETURN NUMBER
);
/
Error report:
02303 - "cannot drop or replace a type with type or table dependents"

Yeah, this is not going to work – we are not allowed to change the definition of our object type because there is a dependent nested table type. So, is this it? Fear not, we have another option.

Data of ANYDATA Datatype as Argument’s Type. Ouch.

Oracle offers a type called ANYDATA, which is a self-describing type – it stores both an instance of some other type and its description. It can even be persisted into a table.

So how can this undecided fellow help us?

We can define the argument of the static function as ANYDATA, and then, pass as an actual argument an instance of ANYDATA containing an array of objects of our type! Then, inside our static function, we will use a member function of ANYDATA type called GetCollection, which will return the objects it holds – in this case, an array of objects of our type.

Below is a simple presentation of this solution.

Step 1: Declare our object type again

CREATE OR REPLACE 
TYPE my_object AS OBJECT (
  some_number NUMBER,
  STATIC FUNCTION static_test_function(
					p_my_objects_tab IN ANYDATA) RETURN NUMBER
);
/
> TYPE MY_OBJECT compiled

Notice that now the type of the argument is ANYDATA.

Step 2: Create nested table type

CREATE TYPE my_objects_tab_t AS TABLE OF my_object;
/
> TYPE MY_OBJECTS_TAB_T compiled

Step 3: Extract my_objects_tab_t object from ANYDATA

CREATE OR REPLACE
TYPE BODY my_object AS

  STATIC FUNCTION static_test_function(
                                    p_my_objects_tab IN ANYDATA) RETURN NUMBER
  AS
    v_my_objects_tab my_objects_tab_t;
    v_dummy NUMBER;
    v_result NUMBER := 0;
  BEGIN
    -- get the collection from ANYDATA object
    --   v_dummy holds status (succes or not)
    v_dummy := p_my_objects_tab.GetCollection(v_my_objects_tab);

    -- as an example, loop through the list and sum up
    --   the some_number field
    FOR v_i IN v_my_objects_tab.FIRST..v_my_objects_tab.LAST
    LOOP
      v_result := v_result + v_my_objects_tab(v_i).some_number;
    END LOOP;

    RETURN v_result;
  END;
END;
/
> TYPE BODY MY_OBJECT compiled

This is where all the magic happens. In line #13, we use the GetCollection member function of ANYDATA type, which takes as an argument a collection which should be filled with elements held in ANYDATA object. Then, as a test, we loop through elements of our just retrieved nested table and sum up some_number field of each element.

Step 4: Test it!

DECLARE
  v_my_objects_tab my_objects_tab_t;
  v_anydata_with_my_objects_tab ANYDATA;

  v_result NUMBER;
BEGIN
  -- create the collection and populate it with some sample data
  v_my_objects_tab := my_objects_tab_t(my_object(5), my_object(10));

  -- create ANYDATA object from the collection
  v_anydata_with_my_objects_tab :=
                      ANYDATA.ConvertCollection(v_my_objects_tab);

  -- call the static function expecting ANYDATA parameter
  v_result := my_object.static_test_function(
                                   v_anydata_with_my_objects_tab);

  dbms_output.put_line(v_result);
END;
/
> 15

Number “15″ appears in the standard output – seems like it works! In the third line, we define an ANYDATA variable which will contain nested table object. In lines #11 and #12, we utilize the ConvertCollection function of ANYDATA type, which returns an instance of ANYDATA type containing the collection passed as the argument.

Am I an apple? Cause I smell like an orange

You may wonder: what’s going to happen if we pass ANYDATA object holding something that we do not expect?

CREATE TYPE my_str_tab_t IS TABLE OF VARCHAR2(100);
/

DECLARE  
  v_my_str_tab my_str_tab_t;
  v_fake ANYDATA;

  v_result NUMBER;
BEGIN
  v_my_str_tab := my_str_tab_t('A', 'B');
  
  v_fake := ANYDATA.ConvertCollection(v_my_str_tab);

  v_result := my_object.static_test_function(v_fake);

  dbms_output.put_line(v_result);
END;
/
22626. 00000 -  "Type Mismatch while constructing or accessing OCIAnyData"
*Cause:    Type supplied is not matching the type of the AnyData.
           If piece wise construction or access is being attempted, the
           type supplied is not matching the type of the current attribute.

As you might have expected, we got an error – we wanted nested table of our my_object type, and we got strings instead. Can we somehow prevent ourselves from such situations? Not only can we, but we should!

We can check the type of object held within ANYDATA using the GetTypeName function. Let’s improve our static function:

CREATE OR REPLACE
TYPE BODY my_object AS
  STATIC FUNCTION static_test_function(
                    p_my_objects_tab IN ANYDATA) RETURN NUMBER
  AS
    v_my_objects_tab my_objects_tab_t;
    v_dummy NUMBER;
    v_result NUMBER := 0;
  BEGIN
    IF p_my_objects_tab.GetTypeName != 'PK.MY_OBJECTS_TAB_T' THEN
      dbms_output.put_line('Expected "PK.MY_OBJECTS_TAB_T" type, ' ||
                           'got: ' || p_my_objects_tab.GetTypeName);
      RETURN NULL;
    END IF;
    
    -- get the collection from ANYDATA object
    --   v_dummy holds status (succes or not)
    v_dummy := p_my_objects_tab.GetCollection(v_my_objects_tab);

    -- as an example, loop through the list and sum up
    --   the some_number field
    FOR v_i IN v_my_objects_tab.FIRST..v_my_objects_tab.LAST
    LOOP
      v_result := v_result + v_my_objects_tab(v_i).some_number;
    END LOOP;

    RETURN v_result;
  END;
END;
/
> TYPE BODY MY_OBJECT compiled

In line #10, we use the GetTypeName function to check if the type of object inside ANYDATA argument is the one we expect. If not, we print the name of the type we got and return NULL. GetTypeName returns fully qualified name of the type, i. e. with the schema that owns it.

Let’s see if this will prevent us from error this time:

DECLARE  
  v_my_str_tab my_str_tab_t;
  v_fake ANYDATA;

  v_result NUMBER;
BEGIN
  v_my_str_tab := my_str_tab_t('A', 'B');
  
  v_fake := ANYDATA.ConvertCollection(v_my_str_tab);

  v_result := my_object.static_test_function(v_fake);

  dbms_output.put_line(v_result);
END;
/
Expected "PK.MY_OBJECTS_TAB_T" type, got: PK.MY_STR_TAB_T

And it did. We see the type we got – PK.MY_STR_TAB_T.

Further Reading & Useful Links

As it turned out, the trick was to use the ANYDATA type. If you would like to read more about it, you’ll find a link below.

ANYDATA in Oracle Documentation


I hope you enjoyed my article. If you have found any errors in it (even typos), you think that I haven’t explained anything clearly enough or you have an idea how I could make the article better – please, do not hesitate to contact me, or leave a comment.


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