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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="howto-meta2"></a>Update the meta data about a table</h2></div></div></div>
<p>
For a general overview of the mete data problem, see the
Get information about a table's columns section. Updating the meta data
can be done by calling
<a class="link" href="GdaConnection.html#gda-connection-update-meta-store" title="gda_connection_update_meta_store ()">gda_connection_update_meta_store()</a> with a %NULL
"context" argument, but this
call updates the whole meta data which will always do the job, but sometimes one knows that only a
part of the meta data need to be updated. Here is an example of how to use a specific
<a class="link" href="GdaMetaStore.html#GdaMetaContext" title="GdaMetaContext">GdaMetaContext</a> argument.
</p>
<p>
Specifically the following code
updates the meta data regarding the "customers" table:
</p>
<pre class="programlisting">
GdaConnection *connection=...
GError *error = NULL;
GValue *table;
GdaMetaContext *mcontext = gda_meta_context_new ();
/* This is a table in the dababase schema for Meta Store to update */
gda_meta_context_set_table ("_tables");
/* Next setup a value to be used as the column in the last table to be used as a condition in the update
in this case we will use the column 'table_name' and update for 'customers'*/
table = gda_value_new (G_TYPE_STRING);
g_value_set_string (table, "customers");
gda_meta_context_set_column ("table_name", table);
gboolean result;
result = gda_connection_update_meta_store (connection, mcontext, &error);
gda_value_free (table);
gda_meta_context_free (mcontext);
if (!result) {
/* handle the error */
g_error_free (error);
}
</pre>
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<p>
Internally <a class="link" href="GdaSqlParser.html#gda-sql-identifier-quote" title="gda_sql_identifier_quote ()">gda_meta_context_set_column()</a> calls
<a class="link" href="GdaSqlParser.html#gda-sql-identifier-quote" title="gda_sql_identifier_quote ()">gda_sql_identifier_quote()</a> which ensure that the contents of
<code class="code">mcontext.column_values</code> values is conform to the convention used by the
<a class="link" href="GdaMetaStore.html" title="GdaMetaStore">GdaMetaStore</a> to represent SQL identifiers when the
values represent an SQL identifier (which is the case in the example above). For more information,
see the <a class="link" href="information_schema.html#information_schema:sql_identifiers" title="SQL identifiers">meta data section about SQL identifiers</a>.
Even though not strictly necessary, it used all the time.
For example if the table name for which a meta data update is requested had been <span class="emphasis"><em>"Customers"</em></span>
(note the upper case C at the beginning and the double quotes) because this is how the database know it, then
not using <a class="link" href="GdaSqlParser.html#gda-sql-identifier-quote" title="gda_sql_identifier_quote ()">gda_sql_identifier_quote()</a> may not have done as
expected.
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