## GdaMetaStore

GdaMetaStore — Dictionary object

## Synopsis

                        GdaMetaStore;
    enum                GdaMetaStoreError;
                        GdaMetaStoreChange;
    enum                GdaMetaStoreChangeType;
                        GdaMetaContext;
    GdaMetaStore *      gda_meta_store_new                  (const gchar *cnc_string);
    GdaMetaStore *      gda_meta_store_new_with_file        (const gchar *file_name);
    gint                gda_meta_store_get_version          (GdaMetaStore *store);
    gchar *             gda_meta_store_sql_identifier_quote (const gchar *id,
                                                             GdaConnection *cnc);
    GdaDataModel *      gda_meta_store_extract              (GdaMetaStore *store,
                                                             const gchar *select_sql,
                                                             GError **error,
                                                             ...);
    GdaMetaStruct *     gda_meta_store_schema_get_structure (GdaMetaStore *store,
                                                             GError **error);
    gboolean            gda_meta_store_get_attribute_value  (GdaMetaStore *store,
                                                             const gchar *att_name,
                                                             gchar **att_value,
                                                             GError **error);
    gboolean            gda_meta_store_set_attribute_value  (GdaMetaStore *store,
                                                             const gchar *att_name,
                                                             const gchar *att_value,
                                                             GError **error);
    gboolean            gda_meta_store_schema_add_custom_object
                                                            (GdaMetaStore *store,
                                                             const gchar *xml_description,
                                                             GError **error);
    GdaConnection *     gda_meta_store_get_internal_connection
                                                            (GdaMetaStore *store);

## Object Hierarchy

      GObject
       +----GdaMetaStore

## Properties

      "catalog"                  gchar*                : Write / Construct Only
      "cnc"                      GdaConnection*        : Read / Write / Construct Only
      "cnc-string"               gchar*                : Write / Construct Only
      "schema"                   gchar*                : Write / Construct Only

## Signals

      "meta-changed"                                   : Run First
      "meta-reset"                                     : Run First
      "suggest-update"                                 : Run Last

## Description

Previous versions of Libgda relied on an XML based file to store dictionary information, such as the database's schema (tables, views, etc) and various other information. The problems were that it was difficult for an application to integrate its own data into the dictionary and that there were some performances problems as the XML file needed to be parsed (and converted into its own in-memory structure) before any data could be read out of it.

The new dictionary now relies on a database structure to store its data (see the database schema section for a detailed description). The actual database can be a single file (using an SQLite database), an entirely in memory database (also using an SQLite database), or a more conventional backend such as a PostgreSQL database for a shared dictionary on a server.

The GdaMetaStore object is thread safe.

## Details

### GdaMetaStore

    typedef struct _GdaMetaStore GdaMetaStore;

### enum GdaMetaStoreError

    typedef enum {
    	GDA_META_STORE_INCORRECT_SCHEMA_ERROR,
    	GDA_META_STORE_UNSUPPORTED_PROVIDER_ERROR,
    	GDA_META_STORE_INTERNAL_ERROR,
    	GDA_META_STORE_META_CONTEXT_ERROR,
    	GDA_META_STORE_MODIFY_CONTENTS_ERROR,
    	GDA_META_STORE_EXTRACT_SQL_ERROR,
    	GDA_META_STORE_ATTRIBUTE_NOT_FOUND_ERROR,
    	GDA_META_STORE_ATTRIBUTE_ERROR,
    	GDA_META_STORE_SCHEMA_OBJECT_NOT_FOUND_ERROR,
    	GDA_META_STORE_SCHEMA_OBJECT_CONFLICT_ERROR,
    	GDA_META_STORE_SCHEMA_OBJECT_DESCR_ERROR,
    	GDA_META_STORE_TRANSACTION_ALREADY_STARTED_ERROR
    } GdaMetaStoreError;

### GdaMetaStoreChange

    typedef struct {
    	/* change general information */
    	GdaMetaStoreChangeType  c_type;
    	gchar                  *table_name;
    	GHashTable             *keys; /* key = ('+' or '-') and a column position in @table (string) starting at 0,
    	                               * value = a GValue pointer */
    } GdaMetaStoreChange;

### enum GdaMetaStoreChangeType

    typedef enum {
    	GDA_META_STORE_ADD,
    	GDA_META_STORE_REMOVE,
    	GDA_META_STORE_MODIFY
    } GdaMetaStoreChangeType;

### GdaMetaContext

    typedef struct {
    	gchar                  *table_name;
    	gint                    size;
    	gchar                 **column_names;
    	GValue                **column_values;
    } GdaMetaContext;

The GdaMetaContext represents a meta data modification context: the how when used with `gda_meta_store_modify_with_context()`, and the what when used with `gda_connection_update_meta_store()`.

gchar *`table_name`; | the name of the table in the GdaMetaStore's internal database
gint `size`; | the size of the `column_names` and `column_values` arrays
gchar **`column_names`; | an array of column names (columns of the `table_name` table)
GValue **`column_values`; | an array of values, one for each column named in `column_names`

### gda_meta_store_new ()

    GdaMetaStore *      gda_meta_store_new                  (const gchar *cnc_string);

Create a new GdaMetaStore object.

`cnc_string` : | a connection string, or `NULL` for an in-memory internal database
Returns : | the newly created object, or `NULL` if an error occurred. [transfer full]

### gda_meta_store_new_with_file ()

    GdaMetaStore *      gda_meta_store_new_with_file        (const gchar *file_name);

Create a new GdaMetaStore object using `file_name` as its internal database

`file_name` : | a file name
Returns : | the newly created object, or `NULL` if an error occurred. [transfer full]

### gda_meta_store_get_version ()

    gint                gda_meta_store_get_version          (GdaMetaStore *store);

Get `store`'s internal schema's version

`store` : | a GdaMetaStore object
Returns : | the version (incremented each time the schema changes, backward compatible)

### gda_meta_store_sql_identifier_quote ()

    gchar *             gda_meta_store_sql_identifier_quote (const gchar *id,
                                                             GdaConnection *cnc);

Use this method to get a correctly quoted (if necessary) SQL identifier which can be used to retrieve or filter information in a GdaMetaStore which stores meta data about `cnc`.

The returned SQL identifier can be used in conjunction with `gda_connection_update_meta_store()`, `gda_connection_get_meta_store_data()`, `gda_connection_get_meta_store_data_v()` and `gda_meta_store_extract()`.

`id` : | an SQL identifier
`cnc` : | a GdaConnection
Returns : | a new string, to free with `g_free()` once not needed anymore. [transfer full]

Since 4.0.3

### gda_meta_store_extract ()

    GdaDataModel *      gda_meta_store_extract              (GdaMetaStore *store,
                                                             const gchar *select_sql,
                                                             GError **error,
                                                             ...);

Extracts some data stored in `store` using a custom SELECT query. If the `select_sql` filter involves SQL identifiers (such as table or column names), then the values should have been adapted using `gda_meta_store_sql_identifier_quote()`.

For more information about SQL identifiers are represented in `store`, see the meta data section about SQL identifiers.

`store` : | a GdaMetaStore object
`select_sql` : | a SELECT statement
`error` : | a place to store errors, or `NULL`. [allow-none]
`...` : | a list of (variable name (gchar *), GValue *value) terminated with NULL, representing values for all the variables mentioned in `select_sql`. If there is no variable then this part can be omitted.
Returns : | a new GdaDataModel, or `NULL` if an error occurred. [transfer full]

### gda_meta_store_schema_get_structure ()

    GdaMetaStruct *     gda_meta_store_schema_get_structure (GdaMetaStore *store,
                                                             GError **error);

Creates a new GdaMetaStruct object representing `store`'s internal database structure.

`store` : | a GdaMetaStore object
`error` : | a place to store errors, or `NULL`. [allow-none]
Returns : | a new GdaMetaStruct object, or `NULL` if an error occurred. [transfer full]

### gda_meta_store_get_attribute_value ()

    gboolean            gda_meta_store_get_attribute_value  (GdaMetaStore *store,
                                                             const gchar *att_name,
                                                             gchar **att_value,
                                                             GError **error);

The GdaMetaStore object maintains a list of (name,value) attributes (attributes names starting with a '_' character are for internal use only and cannot be altered). This method and the `gda_meta_store_set_attribute_value()` method allows the user to add, set or remove attributes specific to their usage.

This method allows to get the value of a attribute stored in `store`. The returned attribute value is placed at `att_value`, the caller is responsible for free that string.

If there is no attribute named `att_name` then `att_value` is set to `NULL` and `error` will contain the GDA_META_STORE_ATTRIBUTE_NOT_FOUND_ERROR error code, and FALSE is returned.

`store` : | a GdaMetaStore object
`att_name` : | name of the attribute to get
`att_value` : | the place to store the attribute value. [out]
`error` : | a place to store errors, or `NULL`. [allow-none]
Returns : | TRUE if no error occurred

### gda_meta_store_set_attribute_value ()

    gboolean            gda_meta_store_set_attribute_value  (GdaMetaStore *store,
                                                             const gchar *att_name,
                                                             const gchar *att_value,
                                                             GError **error);

Set the value of the attribute named `att_name` to `att_value`; see `gda_meta_store_get_attribute_value()` for more information.

`store` : | a GdaMetaStore object
`att_name` : | name of the attribute to set
`att_value` : | value of the attribute to set, or `NULL` to unset the attribute. [allow-none]
`error` : | a place to store errors, or `NULL`. [allow-none]
Returns : | TRUE if no error occurred

### gda_meta_store_schema_add_custom_object ()

    gboolean            gda_meta_store_schema_add_custom_object
                                                            (GdaMetaStore *store,
                                                             const gchar *xml_description,
                                                             GError **error);

The internal database used by `store` can be 'augmented' with some user-defined database objects (such as tables or views). This method allows one to add a new database object.

If the internal database already contains the object, then:

- if the object is equal to the provided description then TRUE is returned

- if the object exists but differs from the provided description, then FALSE is returned, with the GDA_META_STORE_SCHEMA_OBJECT_CONFLICT_ERROR error code

The `xml_description` defines the table of view's definition, for example:

    <table name="mytable">
        <column name="id" pkey="TRUE"/>
        <column name="value"/>
    </table>

The partial DTD for this XML description of the object to add is the following (the top node must be a <table> or a <view>):

    <!ELEMENT table (column*,check*,fkey*,unique*)>
    <!ATTLIST table
              name NMTOKEN #REQUIRED>

    <!ELEMENT column EMPTY>
    <!ATTLIST column
              name NMTOKEN #REQUIRED
              type CDATA #IMPLIED
              pkey (TRUE|FALSE) #IMPLIED
              autoinc (TRUE|FALSE) #IMPLIED
              nullok (TRUE|FALSE) #IMPLIED>

    <!ELEMENT check (#PCDATA)>

    <!ELEMENT fkey (part+)>
    <!ATTLIST fkey
              ref_table NMTOKEN #REQUIRED>

    <!ELEMENT part EMPTY>
    <!ATTLIST part
              column NMTOKEN #IMPLIED
              ref_column NMTOKEN #IMPLIED>

    <!ELEMENT unique (column*)>

    <!ELEMENT view (definition)>
    <!ATTLIST view
              name NMTOKEN #REQUIRED
              descr CDATA #IMPLIED>

    <!ELEMENT definition (#PCDATA)>

`store` : | a GdaMetaStore object
`xml_description` : | an XML description of the table or view to add to `store`
`error` : | a place to store errors, or `NULL`. [allow-none]
Returns : | TRUE if the new object has sucessfully been added

### gda_meta_store_get_internal_connection ()

    GdaConnection *     gda_meta_store_get_internal_connection
                                                            (GdaMetaStore *store);

Get a pointer to the GdaConnection object internally used by `store` to store its contents.

The returned connection can be used to access some other data than the one managed by `store` itself. The returned object is not owned by the caller (if you need to keep it, then use `g_object_ref()`). Do not close the connection.

`store` : | a GdaMetaStore object
Returns : | a GdaConnection, or `NULL`. [transfer none]

## Property Details

### The `"catalog"` property

      "catalog"                  gchar*                : Write / Construct Only

Catalog in which the database objects will be created.

Default value: NULL

### The `"cnc"` property

      "cnc"                      GdaConnection*        : Read / Write / Construct Only

Connection object internally used.

### The `"cnc-string"` property

      "cnc-string"               gchar*                : Write / Construct Only

Connection string for the internal connection to use.

Default value: NULL

### The `"schema"` property

      "schema"                   gchar*                : Write / Construct Only

Schema in which the database objects will be created.

Default value: NULL

## Signal Details

### The `"meta-changed"` signal

    void                user_function                      (GdaMetaStore *store,
                                                            GdaSList     *changes,
                                                            gpointer      user_data)      : Run First

This signal is emitted when the `store`'s contents have changed (the changes are in the `changes` list)

`store` : | the GdaMetaStore instance that emitted the signal
`changes` : | a list of changes made, as a GSList of pointers to GdaMetaStoreChange (which must not be modified)
`user_data` : | user data set when the signal handler was connected.

### The `"meta-reset"` signal

    void                user_function                      (GdaMetaStore *store,
                                                            gpointer      user_data)      : Run First

This signal is emitted when the `store`'s contents have been reset completely and when no detailed changes are available

`store` : | the GdaMetaStore instance that emitted the signal
`user_data` : | user data set when the signal handler was connected.

### The `"suggest-update"` signal

    GdaError*           user_function                      (GdaMetaStore   *store,
                                                            GdaMetaContext *suggest,
                                                            gpointer        user_data)      : Run Last

This signal is emitted when the contents of a table should be updated (data to update or insert only; deleting data is done automatically). This signal is used for internal purposes by the GdaConnection object.

`store` : | the GdaMetaStore instance that emitted the signal
`suggest` : | the suggested update, as a GdaMetaContext structure
`user_data` : | user data set when the signal handler was connected.
Returns : | a new GError error structure if there was an error when processing the signal, or `NULL` if signal propagation should continue