MySQL Connector/C++ 2.0.4
MySQL connector library for C and C++ applications
Connector/C++ implements a plain C interface, called XAPI, which offers functionality similar to that of X DevAPI and which can be used by applications written in plain C. XAPI allows one to work with MySQL Servers implementing a document store via the X Plugin. One can also execute plain SQL queries using this API.
To get started, check out some of the main XAPI functions:
mysqlx_get_session_xxx()functions. These functions return a pointer to an opaque session handle of type
mysqlx_session_t. To execute SQL queries one needs to create a so called "node session" with
mysqlx_get_node_session_xxx()functions. See the X DevAPI Reference for discussion about differences between regular and node sessions.
mysqlx_get_table()function. One first needs to obtain a schema handle with the
mysqlx_collection_find(), or one can create a statement handle with a function like
mysqlx_collection_find_new()and execute it later with
mysqlx_execute()after specifying additional statement parameters.
mysqlx_stmt_bind()before statement is executed.
mysqlx_sql()which requires a handle to a node session.
?placeholders whose values need to be specified either with
mysqlx_stmt_bind(), prior to query execution, or directly in the function
mysqlx_sql_param()which executes such a query.
mysqlx_result_t. It can be used to fetch result's data with functions
mysqlx_json_fetch_one(). It can be also used to examine the result metadata (in case of results of table queries) with the
mysqlx_column_get_xxxfamily of functions.
mysqlx_get_xxx()functions, conversion from database types to the indicated C native type is performed. Both types must match, otherwise result might be corrupted (there are no automatic type conversions). It is also possible to get raw bytes representing the value using the
Many functions in XAPI have a variable parameters list allowing passing arguments in a flexible way. A good illustration of this approach is binding values to
? placeholders in an SQL query. The function
mysqlx_stmt_bind() can bind the corresponding values to all parameters in just one call. For example:
There are several things to keep in mind:
PARAM_TTT()macros. It is important to use the correct macro for each type such as
PARAM_DOUBLE(v_double)can only be used if
v_doubleis declared to have type
PARAM_STRING(v_str)can only be used on
PARAM_ENDas the last parameter and in this way mark the end of the variable parameters list. Failure to do so cannot be detected at the build time, but it will most likely result in an abnormal program termination.
A more complete example of code that access MySQL Database using the XAPI is presented below. See also the list of XAPI Functions.
The following plain C application uses XAPI to connect to a MySQL Server with X Plugin, create a table, add a few rows into it using different ways such as plain SQL with parameters and table INSERT statements. Next, the code reads the table rows and displays the result.
The sample code can be found in file
testapp/xapi_test.cc in the source distribution of Connector/C++ 2.0. See Using Connector/C++ 2.0 for instructions on how to build the sample code.
Code which uses the Connector/C++ XAPI should include the
Checking for errors is an essential part of any program, but in this sample code it can take too much space, therefore we introduce the convenience macros that check for statement errors, result errors and general errors:
Start with creating a session handle using one of the
mysqlx_get_node_session_xxx() functions. We create a node session to be able to execute SQL queries. Session parameters are given using
mysqlx URL. Default URL specifies session on the local host as user
If session could not be established,
mysqlx_get_node_session_from_url() returns NULL handle while error message and code are stored in provided buffers.
Once created, the session is ready to be used. If the session cannot be established the program prints the error and exits.
Use the session to execute SQL queries – here we create a test table. After executing a query, we check its status with the
RESULT_CHECK() macro (which checks if returned result handle is not NULL).
MYSQLX_NULL_TERMINATED, which directs the function to determine the query string length using its own means.
The plain SQL queries executed before did not have any parameters. Next thing to do is to execute an SQL insert statement with
? placeholders. One way of doing this is to first create a statement handle with
mysqlx_sql_new(). Such statement is not executed right away – it will be executed later, after binding the placeholder values first.
The placeholder values for the above statement are specified through a call to the
mysqlx_stmt_bind() function. Parameters list consists of <type, value> pairs. We use convenience macros
PARAM_TTT() to generate such pairs. The list of placeholder values is terminated with
MYSQLX_TYPE_SINTindicates that the next parameter will have the type of signed 64-bit integer (in this case
Once the placeholder values are specified, the statement can be executed with
mysqlx_execute(). Attempt to execute statement with placeholders, without binding values to these placeholders will result in an error. Similar, if the number of bound values is less than the number of placeholders, the attempt to execute such a statement will result in an error. The fact that all placeholders are bound to values is checked only when the statement is executed, not when binding the values.
For the purpose of demonstration we will insert the next row using a specialized table INSERT statement. First, get a handle to the table object with
mysqlx_get_table() functions. The third parameter to these functions is a Boolean flag specifying if an error should be reported if indicated objects do not exist in the database. Without such a check it is possible to create a handle to a non-existing object but then the handle creation is cheap and does not involve any communication with the database. Errors would be reported later, when one attempts to execute a statement for such a non-existent handle.
Create a table INSERT statement using
The next step is to provide the row data using the
mysqlx_set_insert_row() function, which can be called multiple times on the same statement handle before the statement is executed. In this way a multi-row insert will be performed.
In our example we will do a single-row insert. Same as in case of
mysqlx_stmt_bind() the row data is specified as <type, value> pairs and the list of function parameters is terminated by
PARAM_END. After specifying the row data, the insert statement is executed:
After the inserts are finished the code will read the rows. To do so execute table SELECT statement with
mysqlx_table_select_limit(). This limits the number of returned rows to 500:
mysqlx_table_select_limit() executes the statement right away, returning its result. Before we were first creating a statement handle, then adding information to the statement and then executing it.
Now fetch rows one by one. Function
mysqlx_row_fetch_one() returns NULL handle when there are no more rows in the result:
The actual data is read using
mysqlx_get_xxx() functions. These functions return the values through the output parameters.
Along with the data the code can get metadata such as the column names. In this example we just print the column name returned by
Close the session using
mysqlx_session_close(). This implicitly frees all handles associated with the session (results, rows, etc):
The complete code of the example is presented below:
A sample output produced by this code: