GdaReferer

## GdaReferer GdaReferer — Interface to know when on object is completely defined |

## Synopsis

                GdaReferer;
    gboolean    gda_referer_activate            (GdaReferer *iface);
    void        gda_referer_deactivate          (GdaReferer *iface);
    gboolean    gda_referer_is_active           (GdaReferer *iface);
    GSList*     gda_referer_get_ref_objects     (GdaReferer *iface);
    void        gda_referer_replace_refs        (GdaReferer *iface,
                                                 GHashTable *replacements);

## Object Hierarchy

      GInterface
       +----GdaReferer

## Prerequisites

GdaReferer requires GObject.

## Known Implementations

GdaReferer is implemented by GdaQueryFieldValue, GdaQueryCondition, GdaParameter, GdaQueryFieldFunc, GdaQueryFieldAll, GdaQueryTarget, GdaQueryJoin, GdaQueryFieldAgg, GdaDictConstraint, GdaQuery and GdaQueryFieldField.

## Signal Prototypes

    "activated" void        user_function      (GdaReferer *gdareferer,
                                                gpointer user_data);
    "deactivated"
                void        user_function      (GdaReferer *gdareferer,
                                                gpointer user_data);

## Description

Some objects can be initialized in an uncomplete state. This is the case for example of a primary key database constraint, when we don't know, at creation time, which field it applies to. These objects implement this interface to at least signal when they are ready to be used.

Also some objects need to be created <b>before</b> other objects they will need to be operational even exist; they implement this interface.

This interface is particularly important for the GdaQuery and related objects: the individual components of a query are completely defined when they reference objects defined in a data dictionary (a GdaDict object). When any of the components of a query relates to an element not defined in a dictionary, the query can still be used but it's not completely defined.

## Details

### GdaReferer

    typedef struct _GdaReferer GdaReferer;

### gda_referer_activate ()

    gboolean    gda_referer_activate            (GdaReferer *iface);

Tries to activate the object, does nothing if the object is already active.

`iface` : | an object which implements the GdaReferer interface
Returns : | TRUE if the object is active after the call

### gda_referer_deactivate ()

    void        gda_referer_deactivate          (GdaReferer *iface);

Deactivates the object. This is the opposite to function `gda_referer_activate()`. If the object is already non active, then nothing happens.

`iface` : | an object which implements the GdaReferer interface

### gda_referer_is_active ()

    gboolean    gda_referer_is_active           (GdaReferer *iface);

Get the status of an object

`iface` : | an object which implements the GdaReferer interface
Returns : | TRUE if the object is active

### gda_referer_get_ref_objects ()

    GSList*     gda_referer_get_ref_objects     (GdaReferer *iface);

Get the list of objects which are referenced by `iface`. The returned list is a new list. If `iface` is not active, then the returned list is incomplete.

`iface` : | an object which implements the GdaReferer interface
Returns : | a new list of referenced objects

### gda_referer_replace_refs ()

    void        gda_referer_replace_refs        (GdaReferer *iface,
                                                 GHashTable *replacements);

Ask `iface` to replace references to objects listed as keys in the `replacements` hash table with references to objects of the corresponding value.

It's up to the caller to make sure each pair of (key, value) objects in `replacements` are of the same type, and that it makes sense to procede to the replacement.

The object implementing this interface will accept to do any work only if it is already active.

`iface` : | an object which implements the GdaReferer interface
`replacements` : | a GHashTable

## Signals

### The "activated" signal

    void        user_function                  (GdaReferer *gdareferer,
                                                gpointer user_data);

`dbreferer` : | the object which received the signal.
`user_data` : | user data set when the signal handler was connected.

### The "deactivated" signal

    void        user_function                  (GdaReferer *gdareferer,
                                                gpointer user_data);

`dbreferer` : | the object which received the signal.
`user_data` : | user data set when the signal handler was connected.