GdaVconnectionDataModel

GdaVconnectionDataModel — Virtual connection based on a list of GdaDataModel

Stability Level

Stable, unless otherwise indicated

Signals

void vtable-created Run Last
void vtable-dropped Run Last

Object Hierarchy

    GObject
    ╰── GdaConnection
        ╰── GdaVirtualConnection
            ╰── GdaVconnectionDataModel
                ├── GdaLdapConnection
                ╰── GdaVconnectionHub

Implemented Interfaces

GdaVconnectionDataModel implements GdaLockable.

Description

The GdaVconnectionDataModel is a virtual connection in which GdaDataModel data models can be added or removed, each representing a table in the connection, the gda_vconnection_data_model_add_model() and gda_vconnection_data_model_remove() methods.

Furthermore it is possible to declare tables without any associated data model yet, the real data model being automatically created when the table's data is needed. This allows more dynamic table's contents and filtering optimizations. See the gda_vconnection_data_model_add() and gda_vconnection_data_model_remove() methods. The filtering optimizations are based on SQLite's virtual table optimisations see

SQLite's documentation

for some background information.

Functions

GdaVconnectionDataModelFunc ()

void
(*GdaVconnectionDataModelFunc) (GdaDataModel *Param1,
                                const gchar *Param2,
                                gpointer Param3);

This function is called for every GdaDataModel representing a table in a GdaVconnectionDataModel connection, when using the gda_vconnection_data_model_foreach() method.

Parameters

Param1

a pointer to a GdaDataModel.

[allow-none]

Param2

the name of the table represented by Param1

 

Param3

a data pointer, passed as last ergument to gda_vconnection_data_model_foreach()

 

GdaVconnectionDataModelCreateColumnsFunc ()

GList *
(*GdaVconnectionDataModelCreateColumnsFunc)
                               (GdaVconnectionDataModelSpec *Param1,
                                GError **Param2);

Function called to create the virtual table's columns, as GdaColumn objects.

Parameters

Param1

a pointer to a GdaVconnectionDataModelSpec structure

 

Param2

a place to store errors, or NULL

 

Returns

a new list of GdaColumn objects.

[element-type GdaColumn][transfer full]


GdaVconnectionDataModelCreateModelFunc ()

GdaDataModel *
(*GdaVconnectionDataModelCreateModelFunc)
                               (GdaVconnectionDataModelSpec *Param1);

Function called to create a GdaDataModel object, called when a virtual table's data need to be accessed, and when optimization is not handled.

Parameters

Param1

a pointer to a GdaVconnectionDataModelSpec structure

 

Returns

a new GdaDataModel.

[transfer full]


GdaVconnectionDataModelParseFilterFunc ()

void
(*GdaVconnectionDataModelParseFilterFunc)
                               (GdaVconnectionDataModelSpec *Param1,
                                GdaVconnectionDataModelFilter *Param2);

This function actually analyses the proposed optimization and modified Param2 to tell the database engine how (if applicable) it implements the optimization.

Parameters

Param1

a pointer to a GdaVconnectionDataModelSpec structure

 

Param2

a pointer to a GdaVconnectionDataModelFilter structure

 

GdaVconnectionDataModelCreateFModelFunc ()

GdaDataModel *
(*GdaVconnectionDataModelCreateFModelFunc)
                               (GdaVconnectionDataModelSpec *Param1,
                                int Param2,
                                const char *Param3,
                                int Param4,
                                GValue **Param5);

Function called to create a GdaDataModel object, called when a virtual table's data need to be accessed, and when optimization is handled.

Parameters

Param1

a pointer to a GdaVconnectionDataModelSpec structure

 

Param2

the index number chosen to actually execute the optimization (from GdaVconnectionDataModelFilter's idxNum attribute)

 

Param3

corresponds to the GdaVconnectionDataModelFilter's idxPointer attribute

 

Param4

size of Param5

 

Param5

an array of GValue, as specified by the GdaVconnectionDataModelFilter's aConstraintUsage's argvIndex value

 

Returns

a new GdaDataModel.

[transfer full]


gda_vconnection_data_model_add ()

gboolean
gda_vconnection_data_model_add (GdaVconnectionDataModel *cnc,
                                GdaVconnectionDataModelSpec *spec,
                                GDestroyNotify spec_free_func,
                                const gchar *table_name,
                                GError **error);

Create a new virtual table named table_name in cnc . The contents of that new table is dictated by what's in spec .

If there is just one GdaDataModel to make appear as a table then the gda_vconnection_data_model_add_model() method is easier to use.

The spec_free_func can (depending on your code) be used to clean memory allocated for spec or spec->data_model .

If an error occurs, then the spec_free_func function is called using spec as argument.

Parameters

cnc

a GdaVconnectionDataModel connection

 

spec

a GdaVconnectionDataModelSpec structure, used AS IS (not copied) and can be modified

 

spec_free_func

function to call when freeing spec , or NULL.

[allow-none]

table_name

the name of the table

 

error

a place to store errors, or NULL

 

Returns

TRUE if no error occurred


gda_vconnection_data_model_add_model ()

gboolean
gda_vconnection_data_model_add_model (GdaVconnectionDataModel *cnc,
                                      GdaDataModel *model,
                                      const gchar *table_name,
                                      GError **error);

Make model appear as a table named table_name in the cnc connection (as if a "CREATE TABLE..." statement was executed, except that the data contained within model is actually used when table_name 's contents is read or written).

For a more general approach, see the gda_vconnection_data_model_add() method.

Parameters

cnc

a GdaVconnectionDataModel connection

 

model

a GdaDataModel

 

table_name

the name of the table

 

error

a place to store errors, or NULL

 

Returns

TRUE if no error occurred


gda_vconnection_data_model_remove ()

gboolean
gda_vconnection_data_model_remove (GdaVconnectionDataModel *cnc,
                                   const gchar *table_name,
                                   GError **error);

Remove the table named table_name in the cnc connection (as if a "DROP TABLE..." statement was executed, except that no data gets destroyed as the associated data model remains the same).

Parameters

cnc

a GdaVconnectionDataModel connection

 

table_name

the name of the table to remove from cnc

 

error

a place to store errors, or NULL

 

Returns

TRUE if no error occurred


gda_vconnection_data_model_get_table_name ()

const gchar *
gda_vconnection_data_model_get_table_name
                               (GdaVconnectionDataModel *cnc,
                                GdaDataModel *model);

Find the name of the table associated to model in cnc

Parameters

cnc

a GdaVconnectionDataModel connection

 

model

a GdaDataModel representing a table within cnc

 

Returns

the table name, or NULL if not found.

[transfer none][allow-none]


gda_vconnection_data_model_get_model ()

GdaDataModel *
gda_vconnection_data_model_get_model (GdaVconnectionDataModel *cnc,
                                      const gchar *table_name);

Find the GdaDataModel object representing the table_name table in cnc . it can return NULL either if no table named table_name exists, or if that table actually exists but no GdaDataModel has yet been created. For a more general approach, use the gda_vconnection_data_model_get().

Parameters

cnc

a GdaVconnectionDataModel connection

 

table_name

a table name within cnc

 

gda_vconnection_data_model_get ()

GdaVconnectionDataModelSpec *
gda_vconnection_data_model_get (GdaVconnectionDataModel *cnc,
                                const gchar *table_name);

Find the GdaVconnectionDataModelSpec specifying how the table named table_name is represented in cnc .

Parameters

cnc

a GdaVconnectionDataModel connection

 

table_name

a table name within cnc

 

Returns

a GdaVconnectionDataModelSpec pointer, of NULL if there is no table named table_name .

[transfer none][allow-none]

Since 4.2.6


gda_vconnection_data_model_foreach ()

void
gda_vconnection_data_model_foreach (GdaVconnectionDataModel *cnc,
                                    GdaVconnectionDataModelFunc func,
                                    gpointer data);

Call func for each table in cnc .

Warning: func will be called for any table present in cnc even if no data model represents the contents of the table (which means the 1st argument of func may be NULL)

Parameters

cnc

a GdaVconnectionDataModel connection

 

func

a GdaVconnectionDataModelFunc function pointer

 

data

data to pass to func calls

 

Types and Values

struct GdaVconnectionDataModel

struct GdaVconnectionDataModel;

struct GdaVconnectionDataModelSpec

struct GdaVconnectionDataModelSpec {
	GdaDataModel                             *data_model;
	GdaVconnectionDataModelCreateColumnsFunc  create_columns_func;
	GdaVconnectionDataModelCreateModelFunc    create_model_func;

	GdaVconnectionDataModelParseFilterFunc    create_filter_func;
	GdaVconnectionDataModelCreateFModelFunc   create_filtered_model_func;
};

This structure holds all the information supplied to declare a virtual table using gda_vconnection_data_model_add(). You don't need to provider pointers for all the functions and for data_model , but the following rules have to be respected:

  • data_model is not NULL and all the function pointers are NULL: this is the situation when the virtual table's contents is defined once by data_model

  • data_model is NULL and create_columns_func is not NULL:

    • create_filtered_model_func is not NULL: this is the situation where the virtual table's associated data model handles filter optimizations. create_model_func is ignored in this case.

    • create_model_func is not NULL: this is the situation where the virtual table's associated data model does not handle filter optimizations

Note that if specifying a create_filtered_model_func , you should also specifiy a create_filter_func function which is actually responsible for analysing the optimization.


struct GdaVconnectionDataModelFilter

struct GdaVconnectionDataModelFilter {
	/* Inputs */
	int nConstraint; /* Number of entries in aConstraint */
	struct GdaVirtualConstraint {
		int iColumn;       /* Column on left-hand side of constraint */
		GdaSqlOperatorType op;  /* Constraint operator, among _EQ, _LT, _LEQ, _GT, _GEQ, _REGEXP */
	} *aConstraint;            /* Table of WHERE clause constraints */
	int nOrderBy;              /* Number of terms in the ORDER BY clause */
	struct GdaVirtualOrderby {
		int iColumn;       /* Column number */
		gboolean desc;     /* TRUE for DESC.  FALSE for ASC. */
	} *aOrderBy;               /* The ORDER BY clause */

	/* Outputs */
	struct GdaVirtualConstraintUsage {
		int argvIndex;     /* if >0, constraint is part of argv to xFilter */
		gboolean omit;     /* Do not code a test for this constraint if TRUE */
	} *aConstraintUsage;
	int idxNum;                /* Number used to identify the index */
	gpointer idxPointer;       /* Pointer used to identify the index */
	gboolean orderByConsumed;  /* TRUE if output is already ordered */
	double estimatedCost;      /* Estimated cost of using this index */
};

This structure contains data which should be analysed to produce a data model (used as data for a virtual table) when a GdaVconnectionDataModelCreateFModelFunc is called. The structure contains an input part (which should not be modified) and and output part (it is closely mapped with SQLite's sqlite3_index_info type).

A pointer to this structure is passed to the GdaVconnectionDataModelParseFilterFunc function and the function has to modify the variables in the output part (marked as *Outputs*).

The idxNum and idxPointer are passed to the GdaVconnectionDataModelCreateFModelFunc function call and they represent nothing specific except that the GdaVconnectionDataModelParseFilterFunc and GdaVconnectionDataModelCreateFModelFunc functions need to agree on their meaning.

See the gda-vconnection-hub.c file for an usage example.

Signal Details

The “vtable-created” signal

void
user_function (GdaVconnectionDataModel *cnc,
               gchar                   *spec,
               gpointer                 user_data)

Signal emitted when a new virtual table has been declared

Parameters

cnc

the GdaVconnectionDataModel connection

 

spec

the GdaVconnectionDataModelSpec for the new virtual table

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last


The “vtable-dropped” signal

void
user_function (GdaVconnectionDataModel *cnc,
               gchar                   *spec,
               gpointer                 user_data)

Signal emitted when a new virtual table has been undeclared

Parameters

cnc

the GdaVconnectionDataModel connection

 

spec

the GdaVconnectionDataModelSpec for the new virtual table

 

user_data

user data set when the signal handler was connected.

 

Flags: Run Last

See Also

The GdaVproviderDataModel provider to use to create such connection objects.