Connector/C++ 2.0 XAPI Reference {#xapi_ref}
================================

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:

- To access data first create a session using one of @link mysqlx_get_session
  `mysqlx_get_session_xxx()`@endlink 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
  @link mysqlx_get_node_session `mysqlx_get_node_session_xxx()`@endlink
  functions. See the [X DevAPI Reference] (@ref devapi_ref) for discussion about
  differences between regular and node sessions.

- To work with documents in a collection or rows in a table, create a
  handle to the collection or the table using the `mysqlx_get_collection()` or
  the `mysqlx_get_table()` function. One first needs to obtain a schema handle
  with the `mysqlx_get_schema()` function.

- Given a handle to a collection or a table object, one can execute queries and
  statements on that object directly, using functions like
  `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.

- Collection or table statements can use named parameters. Values of these
  parameters must be defined using `mysqlx_stmt_bind()` before statement
  is executed.

- To execute SQL, use the function `mysqlx_sql()` which requires a handle to
  a node session.

- SQL queries can contain `?` 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.

- Executing a statement produces a result handle of type `mysqlx_result_t`. It
  can be used to fetch result's data with functions `mysqlx_row_fetch_one()` or
  `mysqlx_json_fetch_one()`. It can be also used to examine the result metadata
  (in case of results of table queries) with the @link mysqlx_column_get_type
  `mysqlx_column_get_xxx`@endlink family of functions.

- Documents are represented as JSON strings. When getting data from rows with
  @link mysqlx_get_sint `mysqlx_get_xxx()`@endlink 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 `mysqlx_get_bytes()` function.

- Data items are fetched from the result one-by-one without storing complete
  result in memory. It is however possible to buffer a complete result with
  the `mysqlx_store_result()` function.

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:

~~~~~~
mysqlx_stmt_bind(stmt, PARAM_SINT(v_sint),
                       PARAM_UINT(v_uint),
                       PARAM_FLOAT(v_float),
                       PARAM_DOUBLE(v_double),
                       PARAM_STRING(v_str),
                       PARAM_END);
~~~~~~

There are several things to keep in mind:

* In order to be able to correctly recognize the native parameter type
  in the parameter list each parameter must carry the type information.
  This is done using `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_double` is declared to have type `double` or
  `PARAM_STRING(v_str)` can only be used on `v_str` declared as `char*`.

* The variable parameters functions in C do not have the means to know the
  exact number of given parameters on their own. Therefore, it is
  the caller's responsibility to put `PARAM_END` as 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] (@ref xapi).


### Sample code which uses Connector/C++ with XAPI ###

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 @ref usage for instructions on how
to build the sample code.

@dontinclude xapi_test.c

Code which uses the Connector/C++ XAPI should include the `mysql_xapi.h` header.

@skipline mysql_xapi.h

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:

@skipline Error processing
@until _WIN32

Start with creating a session handle using one of the
@link mysqlx_get_node_session_from_url `mysqlx_get_node_session_xxx()`@endlink
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 `root`.

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.

@skipline *url =
@skipline conn_error
@until conn_err_code
@skipline get_node_session
@until }

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).

@note If a query is a null-terminated string the query length parameter can
      be `MYSQLX_NULL_TERMINATED`, which directs the function to determine the
      query string length using its own means.

@skipline mysqlx_sql
@until RESULT_CHECK
@until RESULT_CHECK

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.

@skipline mysqlx_sql_new
@until CRUD_CHECK

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 `PARAM_END`.

@skipline stmt_bind
@until IS_OK

@note The type identifier of the parameter must correspond to the actual C type
  of the value. Otherwise the parameters stack might be corrupted. For instance
  `MYSQLX_TYPE_SINT` indicates that the next parameter will have the type of
  signed 64-bit integer (in this case `v_sint` declared as `int64_t`).

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.

@skipline mysqlx_execute
@until RESULT_CHECK

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_schema()` and `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.

@skipline get_schema
@until RESULT_CHECK
@until RESULT_CHECK

Create a table INSERT statement using `mysqlx_table_insert_new()`.

@skipline mysqlx_table_insert_new

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:

@skipline Change values
@until RESULT_CHECK

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:

@skipline table_select
@until RESULT_CHECK

Note that `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:

@skipline while

The actual data is read using @link mysqlx_get_sint `mysqlx_get_xxx()`@endlink
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
`mysqlx_column_get_name()`:

@skipline {
@until }

Close the session using `mysqlx_session_close()`. This implicitly frees all
handles associated with the session (results, rows, etc):

@skipline mysqlx_session_close

The complete code of the example is presented below:

@include xapi_test.c

A sample output produced by this code:

~~~~~~~
Connected...
Table created...
Rows inserted...

Reading Rows:
Row # 1: [sint: -17] [uint: 101] [flv: 3.310000][dbv: 170000000.000000][strv: just some text [15 bytes]]
Row # 2: [sint: -232] [uint: 789] [flv: 99.339996][dbv: 0.000028][strv: some more text [15 bytes]]
Session closed
~~~~~~~


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