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Relations and Tuples

Relations and Tuples — tables of data which can be indexed on any number of fields

Types and Values

  GRelation
struct GTuples

Includes

#include <glib.h>

Description

A GRelation is a table of data which can be indexed on any number of fields, rather like simple database tables. A GRelation contains a number of records, called tuples. Each record contains a number of fields. Records are not ordered, so it is not possible to find the record at a particular index.

Note that GRelation tables are currently limited to 2 fields.

To create a GRelation, use g_relation_new().

To specify which fields should be indexed, use g_relation_index(). Note that this must be called before any tuples are added to the GRelation.

To add records to a GRelation use g_relation_insert().

To determine if a given record appears in a GRelation, use g_relation_exists(). Note that fields are compared directly, so pointers must point to the exact same position (i.e. different copies of the same string will not match.)

To count the number of records which have a particular value in a given field, use g_relation_count().

To get all the records which have a particular value in a given field, use g_relation_select(). To access fields of the resulting records, use g_tuples_index(). To free the resulting records use g_tuples_destroy().

To delete all records which have a particular value in a given field, use g_relation_delete().

To destroy the GRelation, use g_relation_destroy().

To help debug GRelation objects, use g_relation_print().

GRelation has been marked as deprecated, since this API has never been fully implemented, is not very actively maintained and rarely used.

Functions

g_relation_new ()

GRelation *
g_relation_new (gint fields);

g_relation_new has been deprecated since version 2.26 and should not be used in newly-written code.

Rarely used API

Creates a new GRelation with the given number of fields. Note that currently the number of fields must be 2.

Parameters

fields

the number of fields.

 

Returns

a new GRelation.


g_relation_index ()

void
g_relation_index (GRelation *relation,
                  gint field,
                  GHashFunc hash_func,
                  GEqualFunc key_equal_func);

g_relation_index has been deprecated since version 2.26 and should not be used in newly-written code.

Rarely used API

Creates an index on the given field. Note that this must be called before any records are added to the GRelation.

Parameters

relation

a GRelation.

 

field

the field to index, counting from 0.

 

hash_func

a function to produce a hash value from the field data.

 

key_equal_func

a function to compare two values of the given field.

 

g_relation_insert ()

void
g_relation_insert (GRelation *relation,
                   ...);

g_relation_insert has been deprecated since version 2.26 and should not be used in newly-written code.

Rarely used API

Inserts a record into a GRelation.

Parameters

relation

a GRelation.

 

...

the fields of the record to add. These must match the number of fields in the GRelation, and of type gpointer or gconstpointer.

 

g_relation_exists ()

gboolean
g_relation_exists (GRelation *relation,
                   ...);

g_relation_exists has been deprecated since version 2.26 and should not be used in newly-written code.

Rarely used API

Returns TRUE if a record with the given values exists in a GRelation. Note that the values are compared directly, so that, for example, two copies of the same string will not match.

Parameters

relation

a GRelation.

 

...

the fields of the record to compare. The number must match the number of fields in the GRelation.

 

Returns

TRUE if a record matches.


g_relation_count ()

gint
g_relation_count (GRelation *relation,
                  gconstpointer key,
                  gint field);

g_relation_count has been deprecated since version 2.26 and should not be used in newly-written code.

Rarely used API

Returns the number of tuples in a GRelation that have the given value in the given field.

Parameters

relation

a GRelation.

 

key

the value to compare with.

 

field

the field of each record to match.

 

Returns

the number of matches.


g_relation_select ()

GTuples *
g_relation_select (GRelation *relation,
                   gconstpointer key,
                   gint field);

g_relation_select has been deprecated since version 2.26 and should not be used in newly-written code.

Rarely used API

Returns all of the tuples which have the given key in the given field. Use g_tuples_index() to access the returned records. The returned records should be freed with g_tuples_destroy().

Parameters

relation

a GRelation.

 

key

the value to compare with.

 

field

the field of each record to match.

 

Returns

the records (tuples) that matched.


g_relation_delete ()

gint
g_relation_delete (GRelation *relation,
                   gconstpointer key,
                   gint field);

g_relation_delete has been deprecated since version 2.26 and should not be used in newly-written code.

Rarely used API

Deletes any records from a GRelation that have the given key value in the given field.

Parameters

relation

a GRelation.

 

key

the value to compare with.

 

field

the field of each record to match.

 

Returns

the number of records deleted.


g_relation_destroy ()

void
g_relation_destroy (GRelation *relation);

g_relation_destroy has been deprecated since version 2.26 and should not be used in newly-written code.

Rarely used API

Destroys the GRelation, freeing all memory allocated. However, it does not free memory allocated for the tuple data, so you should free that first if appropriate.

Parameters

relation

a GRelation.

 

g_relation_print ()

void
g_relation_print (GRelation *relation);

g_relation_print has been deprecated since version 2.26 and should not be used in newly-written code.

Rarely used API

Outputs information about all records in a GRelation, as well as the indexes. It is for debugging.

Parameters

relation

a GRelation.

 

g_tuples_destroy ()

void
g_tuples_destroy (GTuples *tuples);

g_tuples_destroy has been deprecated since version 2.26 and should not be used in newly-written code.

Rarely used API

Frees the records which were returned by g_relation_select(). This should always be called after g_relation_select() when you are finished with the records. The records are not removed from the GRelation.

Parameters

tuples

the tuple data to free.

 

g_tuples_index ()

gpointer
g_tuples_index (GTuples *tuples,
                gint index_,
                gint field);

g_tuples_index has been deprecated since version 2.26 and should not be used in newly-written code.

Rarely used API

Gets a field from the records returned by g_relation_select(). It returns the given field of the record at the given index. The returned value should not be changed.

Parameters

tuples

the tuple data, returned by g_relation_select().

 

index_

the index of the record.

 

field

the field to return.

 

Returns

the field of the record.

Types and Values

GRelation

typedef struct _GRelation GRelation;

The GRelation struct is an opaque data structure to represent a Relation. It should only be accessed via the following functions.


struct GTuples

struct GTuples {
  guint len;
};

The GTuples struct is used to return records (or tuples) from the GRelation by g_relation_select(). It only contains one public member - the number of records that matched. To access the matched records, you must use g_tuples_index().

Members

guint len;

the number of records that matched.

 
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