Choice: One to many links.
[Query Object Framework]

Detailed Description

Objects can be linked together one-to-one by simply using the name of the related object as the parameter type in the QofClass parameter list.

{ FOO_PARAM, BAR_ID, (QofAccessFunc)qofFooGetBar, (QofSetterFunc)qofFooSetBar },

This is limited as each FOO entity can contain only one reference to a single BAR entity per parameter. Also, this parameter cannot be used to link to a similar object, OBJ. This requires "one to many" links.

There are two types of one-to-many links in QOF.

  1. QOF_TYPE_COLLECT - one to many entities all of only one type.
  2. QOF_TYPE_CHOICE - one to a single entity of many possible types.

Currently, there is no explicit way to support many-to-many links but existing methods can be combined to give approximately the same results.

A QOF_TYPE_CHOICE object is like a C++ template. QOF_TYPE_CHOICE doesn't really exist by itself:

It holds a single entity of type X, Y, or Z for the purposes of QOF or QSF. For querying the object it queries as if it's an X, Y, or Z.

Each choice type has it's own definition of the allowable objects - each of which need to be registered as normal. Objects can declare themselves to be one option of a particular choice. There is no requirement for any object to be either a choice or an option for a choice object.

  1. Each QOF_TYPE_CHOICE parameter provides access to ONE entity of a pre-determined set of object types.
  2. The entity type within the choice can be determined at run time.
  3. Each entity can have a different *type* of entity to it's siblings, provided that it is one of the pre-determined object types.
  4. Objects declare themselves as containing choices and other objects can add themselves to the list of acceptable choices of suitable objects.
  5. QOF_TYPE_CHOICE is transparent - objects should retrieve the e_type of the received entity and handle the entity appropriately.
  6. The number of different entity types that can be pre-determined for any one QOF_TYPE_CHOICE parameter is not fixed. You can have as many types as the QofAccessFunc and QofSetterFunc can handle.
  7. Any one parameter can only have one QOF type. You cannot have a parameter that is both QOF_TYPE_COLLECT and QOF_TYPE_CHOICE any more than you can have one parameter that is both QOF_TYPE_BOOLEAN and QOF_TYPE_NUMERIC.
  8. When setting references using QOF_TYPE_CHOICE, QOF passes a single entity to the QofSetterFunc and it is left to the function to determine how to handle that entity type. When retrieving references using QOF_TYPE_CHOICE, the object must return a single entity matching one of the choice types.


file  qofchoice.h
 Linking one entity to other entities of many possible types.
gboolean qof_object_is_choice (QofIdType type)
 Does this object contain a choice parameter?
gboolean qof_choice_create (gchar *type)
 Set an object as using QOF_TYPE_CHOICE.
gboolean qof_choice_add_class (gchar *choice, gchar *add, gchar *param_name)
 Add the choices for this parameter to the object.
GList * qof_object_get_choices (QofIdType type, QofParam *param)
 Return the list of all object types usable with this parameter.
gboolean qof_choice_check (gchar *choice_obj, gchar *param_name, gchar *choice)
 Is the choice valid for this param_name?
#define QOF_TYPE_CHOICE   "choice"
 Identify an object as containing a choice.


#define QOF_MOD_CHOICE   "qof-choice"

Define Documentation

#define QOF_TYPE_CHOICE   "choice"

Identify an object as containing a choice.


Definition at line 103 of file qofchoice.h.

Function Documentation

gboolean qof_choice_add_class ( gchar *  choice,
gchar *  add,
gchar *  param_name 

Add the choices for this parameter to the object.

choice The choice object.
add The object to be added as an option.
param_name The parameter that will be used to get or set options.
FALSE if object is not a choice object or on error otherwise TRUE.

Definition at line 75 of file qofchoice.c.

00076 {
00077     GHashTable *param_table;
00078     GList *option_list;
00080     option_list = NULL;
00081     param_table = NULL;
00082     g_return_val_if_fail (select != NULL, FALSE);
00083     g_return_val_if_fail (qof_object_is_choice (select), FALSE);
00084     param_table =
00085         (GHashTable *) g_hash_table_lookup (qof_choice_table, select);
00086     g_return_val_if_fail (param_table, FALSE);
00087     option_list = (GList *) g_hash_table_lookup (param_table, param_name);
00088     option_list = g_list_append (option_list, option);
00089     g_hash_table_insert (param_table, param_name, option_list);
00090     return TRUE;
00091 }

gboolean qof_choice_check ( gchar *  choice_obj,
gchar *  param_name,
gchar *  choice 

Is the choice valid for this param_name?

choice_obj The object containing the QOF_TYPE_CHOICE parameter.
param_name The name of a QOF_TYPE_CHOICE parameter in this object.
choice The QofIdType to look for in the list of choices.
TRUE if choice is found in the list of allowed choices for this parameter of this object. Otherwise, FALSE

Definition at line 108 of file qofchoice.c.

00109 {
00110     GList *choices, *result;
00111     GHashTable *param_table;
00113     choices = result = NULL;
00114     g_return_val_if_fail (qof_object_is_choice (choice_obj), FALSE);
00115     param_table = g_hash_table_lookup (qof_choice_table, choice_obj);
00116     choices = g_hash_table_lookup (param_table, param_name);
00117     result = g_list_find (choices, choice);
00118     if (!result)
00119         return FALSE;
00120     return TRUE;
00121 }

GList* qof_object_get_choices ( QofIdType  type,
QofParam param 

Return the list of all object types usable with this parameter.

type The choice object type.
param The name of the parameter that will be used to get or set options.
NULL on error or if no options exist for this parameter, otherwise a GList of all QofIdType object type(s) available via this choice object using this parameter.

Definition at line 94 of file qofchoice.c.

00095 {
00096     GList *choices;
00097     GHashTable *param_table;
00099     g_return_val_if_fail (type != NULL, NULL);
00100     g_return_val_if_fail (qof_choice_is_initialized () == TRUE, FALSE);
00101     choices = NULL;
00102     param_table = g_hash_table_lookup (qof_choice_table, type);
00103     choices = g_hash_table_lookup (param_table, param->param_name);
00104     return choices;
00105 }

gboolean qof_object_is_choice ( QofIdType  type  ) 

Does this object contain a choice parameter?

Returns TRUE if any parameter in the object definition uses a choice of elements, whether or not those parameters contain any data.

type Type of object/entity.
TRUE if one or more choice parameters has been registered using the object definition, otherwise FALSE.

Definition at line 45 of file qofchoice.c.

00046 {
00047     gpointer value, check;
00049     value = NULL;
00050     check = NULL;
00051     if (!qof_choice_is_initialized ())
00052         return FALSE;
00053     g_return_val_if_fail (type != NULL, FALSE);
00054     value = g_hash_table_lookup (qof_choice_table, type);
00055     if ((GHashTable *) value)
00056         return TRUE;
00057     return FALSE;
00058 }

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