## GdaVconnectionDataModel

GdaVconnectionDataModel — Virtual connection based on a list of GdaDataModel

## Synopsis

    struct              GdaVconnectionDataModel;
    void                (*GdaVconnectionDataModelFunc)      (GdaDataModel *Param1,
                                                             const gchar *Param2,
                                                             gpointer Param3);
    struct              GdaVconnectionDataModelSpec;
    GList *             (*GdaVconnectionDataModelCreateColumnsFunc)
                                                            (GdaVconnectionDataModelSpec *Param1,
                                                             GError **Param2);
    GdaDataModel *      (*GdaVconnectionDataModelCreateModelFunc)
                                                            (GdaVconnectionDataModelSpec *Param1);
    gboolean            gda_vconnection_data_model_add      (GdaVconnectionDataModel *cnc,
                                                             GdaVconnectionDataModelSpec *spec,
                                                             GDestroyNotify spec_free_func,
                                                             const gchar *table_name,
                                                             GError **error);
    gboolean            gda_vconnection_data_model_add_model
                                                            (GdaVconnectionDataModel *cnc,
                                                             GdaDataModel *model,
                                                             const gchar *table_name,
                                                             GError **error);
    gboolean            gda_vconnection_data_model_remove   (GdaVconnectionDataModel *cnc,
                                                             const gchar *table_name,
                                                             GError **error);
    const gchar *       gda_vconnection_data_model_get_table_name
                                                            (GdaVconnectionDataModel *cnc,
                                                             GdaDataModel *model);
    GdaDataModel *      gda_vconnection_data_model_get_model
                                                            (GdaVconnectionDataModel *cnc,
                                                             const gchar *table_name);
    GdaVconnectionDataModelSpec * gda_vconnection_data_model_get
                                                            (GdaVconnectionDataModel *cnc,
                                                             const gchar *table_name);
    void                gda_vconnection_data_model_foreach  (GdaVconnectionDataModel *cnc,
                                                             GdaVconnectionDataModelFunc func,
                                                             gpointer data);

## Object Hierarchy

      GObject
       +----GdaConnection
             +----GdaVirtualConnection
                   +----GdaVconnectionDataModel
                         +----GdaLdapConnection
                         +----GdaVconnectionHub

## Implemented Interfaces

GdaVconnectionDataModel implements GdaLockable.

## Signals

      "vtable-created"                                 : Run Last
      "vtable-dropped"                                 : Run Last

## Description

the GdaVconnectionDataModel is a virtual connection in which GdaDataModel data models can bas added or removed, each representing a table in the connection.

Note that virtual connections have some inherent limitations [2]due to the implementation.

## Details

### struct GdaVconnectionDataModel

    struct GdaVconnectionDataModel;

### 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.

`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()`

### 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.

GdaDataModel *`data_model`; | a GdaDataModel, or `NULL`. [allow-none]
GdaVconnectionDataModelCreateColumnsFunc `create_columns_func`; | a pointer to a GdaVconnectionDataModelCreateColumnsFunc function, or `NULL`. [allow-none]
GdaVconnectionDataModelCreateModelFunc `create_model_func`; | a pointer to a GdaVconnectionDataModelCreateModelFunc function, or `NULL`. [allow-none]
GdaVconnectionDataModelParseFilterFunc `create_filter_func`; | a pointer to a GdaVconnectionDataModelParseFilterFunc function, or `NULL`. [allow-none]
GdaVconnectionDataModelCreateFModelFunc `create_filtered_model_func`; | a pointer to a GdaVconnectionDataModelCreateFModelFunc function, or `NULL`. [allow-none]

### GdaVconnectionDataModelCreateColumnsFunc ()

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

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

`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.

`Param1` : | a pointer to a GdaVconnectionDataModelSpec structure
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.

`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.

`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).

`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`

`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()`.

`cnc` : | a GdaVconnectionDataModel connection
`table_name` : | a table name within `cnc`
Returns : | the GdaDataModel, or `NULL`. [transfer none][allow-none]

### 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`.

`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`)

`cnc` : | a GdaVconnectionDataModel connection
`func` : | a GdaVconnectionDataModelFunc function pointer
`data` : | data to pass to `func` calls

## Signal Details

### The `"vtable-created"` signal

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

Signal emitted when a new virtual table has been declared

`cnc` : | the GdaVconnectionDataModel connection
`spec` : | the GdaVconnectionDataModelSpec for the new virtual table
`user_data` : | user data set when the signal handler was connected.

### The `"vtable-dropped"` signal

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

Signal emitted when a new virtual table has been undeclared

`cnc` : | the GdaVconnectionDataModel connection
`spec` : | the GdaVconnectionDataModelSpec for the new virtual table
`user_data` : | user data set when the signal handler was connected.

## See Also

The GdaVproviderDataModel provider to use to create such connection objects.

[2] As virtual connections are implemented using SQLite's virtual table features, the SQL dialect which can be used is the SQLite one (see the SQL as Understood By SQLite page), and there are a few limitations inherent to this implementation (see link for more information).

Also note that it is possible to create temporary tables in virtual connections using "CREATE TEMP TABLE..." statements, but the contents of such tables will be lost once the connection is closed.