Top |
GdaDataSelectGdaDataSelect — Base class for data models returned by the execution of a SELECT statement |
gboolean | auto-reset | Read / Write |
GdaConnection * | connection | Read / Write / Construct Only |
GdaStatement * | delete-stmt | Read / Write |
GdaSet * | exec-params | Read / Write / Construct Only |
double | execution-delay | Read / Write |
GdaStatement * | insert-stmt | Read / Write |
guint | model-usage | Read / Write / Construct Only |
GdaPStmt * | prepared-stmt | Read / Write |
GdaStatement * | select-stmt | Read |
gboolean | store-all-rows | Read / Write |
GdaStatement * | update-stmt | Read / Write |
This data model implements the GdaDataModel interface and is the required base object when database providers implement a data model returned when a SELECT statement has been executed. As the GdaDataModel interface is implemented, consult the API to access and modify the data held in a GdaDataSelect object.
Depending on the requested data model usage (as specified by the "model_usage" parameter of the
gda_connection_statement_execute()
and similar
methods, the GdaDataSelect will allow random access, cursor based access or both.
Also, when later you'll be reading the data contained in a GdaDataSelect object, depending on the actual
implementation (which adapts to the API providede by the database server), some calls to the database server
may be necessary to actually obtain the data. If this behaviour is not the one intended and if you need to
access the data without having to contact the database server (for example for performances reasons), then
you can use the gda_data_select_prepare_for_offline()
method or specify the GDA_STATEMENT_MODEL_OFFLINE
flag when executing the SELECT statement.
The default behaviour however is to disallow modifications, and this section documents how to parametrize a GdaDataSelect to allow modifications. Once this is done, any modification done to the data model will be propagated to the modified table in the database using INSERT, UPDATE or DELETE statements.
After any modification, it is still possible to read values from the data model (even values for rows which have been modified or inserted). The data model might then execute some SELECT statement to fetch some actualized values.
Note: there is a corner case where a modification made to a row would make the row not selected at first in the data model (for example is the original SELECT statement included a clause "WHERE id < 100" and the modification sets the "id" value to 110), then the row will still be in the data model even though it would not be if the SELECT statement which execution created the data model in the first place was re-run. This is illustrated in the schema below:
gboolean gda_data_select_set_row_selection_condition_sql (GdaDataSelect *model
,const gchar *sql_where
,GError **error
);
Specifies the SQL condition corresponding to the WHERE part of a SELECT statement which would return only 1 row (the expression of the primary key).
For example for a table created as "CREATE TABLE mytable (part1 int NOT NULL, part2 string NOT NULL,
name string, PRIMARY KEY (part1, part2))", and if pmodel
corresponds to the execution of the
"SELECT name, part1, part2 FROM mytable", then the sensible value for sql_where
would be
"part1 = ##-1::int AND part2 = ##-2::string" because the values of the 'part1' field are located
in pmodel
's column number 1 and the values of the 'part2' field are located
in pmodel
's column number 2 and the primary key is composed of (part1, part2).
For more information about the syntax of the parameters (named "##-1::int" for example), see the
GdaSqlParser documentation, andgda_data_select_set_modification_statement().
model |
a GdaDataSelect data model |
|
sql_where |
an SQL condition (without the WHERE keyword) |
|
error |
a place to store errors, or |
[allow-none] |
gboolean gda_data_select_set_row_selection_condition (GdaDataSelect *model
,GdaSqlExpr *expr
,GError **error
);
Offers the same features as gda_data_select_set_row_selection_condition_sql()
but using a GdaSqlExpr
structure instead of an SQL syntax.
[skip]
model |
a GdaDataSelect data model |
|
expr |
a GdaSqlExpr expression. |
[transfer none] |
error |
a place to store errors, or |
[allow-none] |
gboolean gda_data_select_compute_row_selection_condition (GdaDataSelect *model
,GError **error
);
Offers the same features as gda_data_select_set_row_selection_condition()
but the expression
is computed from the meta data associated to the connection being used when model
was created.
NOTE1: make sure the meta data associated to the connection is up to date before using this
method, see gda_connection_update_meta_store()
.
NOTE2: if the SELECT statement from which model
has been created uses more than one table, or
if the table used does not have any primary key, then this method will fail
gboolean gda_data_select_set_modification_statement (GdaDataSelect *model
,GdaStatement *mod_stmt
,GError **error
);
Informs model
that it should allow modifications to the data in some columns and some rows
using mod_stmt
to propagate those modifications into the database.
If mod_stmt
is:
an UPDATE statement, then all the rows in model
will be writable
a DELETE statement, then it will be possible to delete rows in model
in INSERT statement, then it will be possible to add some rows to model
any other statement, then this method will return an error
This method can be called several times to specify different types of modification statements.
Each modification statement will be executed when one or more values are modified in the data model; each statement should then include variables which will be set to either the old value or the new value of a column at the specified modified row (but can also contain other variables). Each variable named as "+<number>" will be mapped to the new value of the number'th column (starting at 0), and each variable named as "-<number>" will be mapped to the old value of the number'th column.
Examples of the SQL equivalent of each statement are (for example if "mytable" has the "id" field as primary key, and if that field is auto incremented and if the data model is the result of executing "SELECT * from mytable").
"INSERT INTO mytable (name) VALUES (##+1::string)": the column ID can not be set for new rows
"DELETE FROM mytable WHERE id=#<link linkend="0-int"><type>“int”</type></link>"
"UPDATE mytable SET name=##+1::string WHERE id=#<link linkend="0-int"><type>“int”</type></link>": the column ID cannot be modified
Also see the gda_data_select_set_row_selection_condition_sql()
for more information about the WHERE
part of the UPDATE and DELETE statement types.
If mod_stmt
is an UPDATE or DELETE statement then it should have a WHERE part which identifies
a unique row in model
(please note that this property can't be checked but may result
in model
behaving in an unpredictable way).
NOTE1: However, if the gda_data_select_set_row_selection_condition()
or gda_data_select_set_row_selection_condition_sql()
have been successfully be called before, the WHERE
part of mod_stmt
WILL be modified to use the row selection condition specified through one of
these methods (please not that it is then possible to avoid specifying a WHERE part in mod_stmt
then).
NOTE2: if gda_data_select_set_row_selection_condition()
or gda_data_select_set_row_selection_condition_sql()
have not yet been successfully be called before, then
the WHERE part of mod_stmt
will be used as if one of these functions had been called.
model |
a GdaDataSelect data model |
|
mod_stmt |
a GdaStatement (INSERT, UPDATE or DELETE) |
|
error |
a place to store errors, or |
[allow-none] |
gboolean gda_data_select_set_modification_statement_sql (GdaDataSelect *model
,const gchar *sql
,GError **error
);
Offers the same feature as gda_data_select_set_modification_statement()
but using an SQL statement.
model |
a GdaDataSelect data model |
|
sql |
an SQL text |
|
error |
a place to store errors, or |
[allow-none] |
gboolean gda_data_select_compute_modification_statements (GdaDataSelect *model
,GError **error
);
Makes model
try to compute INSERT, UPDATE and DELETE statements to be used when modifying model
's contents.
Note: any modification statement set using gda_data_select_set_modification_statement()
will first be unset
This function is similar to calling gda_data_select_compute_modification_statements_ext()
with
cond_type
set to GDA_DATA_SELECT_COND_PK
gboolean gda_data_select_compute_modification_statements_ext (GdaDataSelect *model
,GdaDataSelectConditionType cond_type
,GError **error
);
Makes model
try to compute INSERT, UPDATE and DELETE statements to be used when modifying model
's contents.
Note: any modification statement set using gda_data_select_set_modification_statement()
will first be unset
model |
a GdaDataSelect data model |
|
cond_type |
the type of condition for the modifications where one row only should be identified |
|
error |
a place to store errors, or |
[allow-none] |
TRUE
if no error occurred. If FALSE
is returned, then some modification statement may still have been computed
Since: 4.2.9
gboolean gda_data_select_compute_columns_attributes (GdaDataSelect *model
,GError **error
);
Computes correct attributes for each of model
's columns, which includes the "NOT NULL" attribute, the
default value, the precision and scale for numeric values.
gboolean gda_data_select_rerun (GdaDataSelect *model
,GError **error
);
Requests that model
be re-run to have an updated result. If an error occurs,
then model
will not be changed.
Since: 4.2
void gda_data_select_add_exception (GdaDataSelect *model
,GError *error
);
Add an exception to model
.
Since: 4.2.6
gboolean gda_data_select_prepare_for_offline (GdaDataSelect *model
,GError **error
);
Use this method to make sure all the data contained in the data model are stored on the client side (and that no subsquent call to the server will be necessary to access that data), at the cost of a higher memory consumption.
This method is useful in the following situations:
You need to disconnect from the server and continue to use the data in the data model
You need to make sure the data in the data model can be used even though the connection to the server may be used for other purposes (for example executing other queries)
Note that this method will fail if:
the data model contains any blobs (because blobs reading requires acces to the server); binary values are Ok, though.
the data model has been modified since it was created
Since: 5.2.0
Defines what criteria gda_data_select_compute_modification_statements_ext()
uses
to uniquely identify a single row in a table when creating modification statements.
“auto-reset”
property“auto-reset” gboolean
Automatically re-run the SELECT statement if any parameter has changed since it was first executed.
Owner: GdaDataSelect
Flags: Read / Write
Default value: FALSE
“connection”
property“connection” GdaConnection *
Connection from which this data model is created.
Owner: GdaDataSelect
Flags: Read / Write / Construct Only
“delete-stmt”
property“delete-stmt” GdaStatement *
DELETE Statement to be executed to remove data.
Owner: GdaDataSelect
Flags: Read / Write
“exec-params”
property“exec-params” GdaSet *
GdaSet used when the SELECT statement was executed.
Owner: GdaDataSelect
Flags: Read / Write / Construct Only
“execution-delay”
property “execution-delay” double
This property stores the execution delay which has been necessary to obtain the data
Owner: GdaDataSelect
Flags: Read / Write
Allowed values: >= 0
Default value: 0
Since: 4.2.9
“insert-stmt”
property“insert-stmt” GdaStatement *
INSERT Statement to be executed to add data.
Owner: GdaDataSelect
Flags: Read / Write
“model-usage”
property“model-usage” guint
Determines how the data model may be used.
Owner: GdaDataSelect
Flags: Read / Write / Construct Only
Allowed values: >= 1
Default value: 1
“prepared-stmt”
property“prepared-stmt” GdaPStmt *
Associated prepared statement (for internal usage).
Owner: GdaDataSelect
Flags: Read / Write
“select-stmt”
property“select-stmt” GdaStatement *
SELECT statement which was executed to yield to the data model.
Owner: GdaDataSelect
Flags: Read
“store-all-rows”
property“store-all-rows” gboolean
Tells if model has analyzed all the rows.
Owner: GdaDataSelect
Flags: Read / Write
Default value: FALSE
“update-stmt”
property“update-stmt” GdaStatement *
UPDATE Statement to be executed to update data.
Owner: GdaDataSelect
Flags: Read / Write