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# mysqlpp::Query Class Reference

A class for building and executing SQL queries. More...

`#include <query.h>`

Inheritance diagram for mysqlpp::Query:

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Collaboration diagram for mysqlpp::Query:

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List of all members.

## Public Types

typedef const SQLString & | ss
| to keep parameter lists short
typedef SQLQueryParms | parms
| shortens def'ns of above macros

## Public Methods

| Query (Connection *c, bool te=true)
| Create a new query object attached to a connection.
MYSQLPP_EXPORT | Query (const Query &q)
| Create a new query object as a copy of another.
MYSQLPP_EXPORT Query & | operator= (const Query &rhs)
| Assign another query's state to this object.
MYSQLPP_EXPORT std::string | error ()
| Get the last error message that was set.
MYSQLPP_EXPORT bool | success ()
| Returns true if the last operation succeeded.
MYSQLPP_EXPORT void | parse ()
| Treat the contents of the query string as a template query.
MYSQLPP_EXPORT void | reset ()
| Reset the query object so that it can be reused.
std::string | preview ()
| Return the query string currently in the buffer.
std::string | preview (SQLQueryParms &p)
| Return the query string currently in the buffer.
std::string | str ()
| Get built query as a null-terminated C++ string.
std::string | str (query_reset r)
| Get built query as a null-terminated C++ string.
MYSQLPP_EXPORT std::string | str (SQLQueryParms &p)
| Get built query as a null-terminated C++ string.
MYSQLPP_EXPORT std::string | str (SQLQueryParms &p, query_reset r)
| Get built query as a null-terminated C++ string.
MYSQLPP_EXPORT bool | exec (const std::string &str)
| Execute a query.
ResNSel | execute ()
| Execute built-up query.
MYSQLPP_EXPORT ResNSel | execute (const char *str)
| Execute query in a C++ string.
ResUse | use ()
| Execute a query that can return a result set.
MYSQLPP_EXPORT ResUse | use (const char *str)
| Execute query in a C++ string.
Result | store ()
| Execute a query that can return a result set.
MYSQLPP_EXPORT Result | store (const char *str)
| Execute query in a C++ string.
MYSQLPP_EXPORT Result | store_next ()
| Return next result set, when processing a multi-query.
MYSQLPP_EXPORT bool | more_results ()
| Return whether more results are waiting for a multi-query or stored procedure response.
template<class Sequence> void | storein_sequence (Sequence &con, query_reset r=RESET_QUERY)
| Execute a query, storing the result set in an STL sequence container.
template<class Set> void | storein_set (Set &con, query_reset r=RESET_QUERY)
| Execute a query, storing the result set in an STL associative container.
template<class Container> void | storein (Container &con, query_reset r=RESET_QUERY)
| Execute a query, and store the entire result set in an STL container.
template<class T> void | storein (std::vector< T > &con, const char *s)
| Specialization of storein_sequence() for `std::vector`.
template<class T> void | storein (std::deque< T > &con, const char *s)
| Specialization of storein_sequence() for `std::deque`.
template<class T> void | storein (std::list< T > &con, const char *s)
| Specialization of storein_sequence() for `std::list`.
template<class T> void | storein (std::set< T > &con, const char *s)
| Specialization of storein_set() for `std::set`.
template<class T> void | storein (std::multiset< T > &con, const char *s)
| Specialization of storein_set() for `std::multiset`.
template<class T> Query & | update (const T &o, const T &n)
| Replace an existing row's data with new data.
template<class T> Query & | insert (const T &v)
| Insert a new row.
template<class Iter> Query & | insert (Iter first, Iter last)
| Insert multiple new rows.
template<class T> Query & | replace (const T &v)
| Insert new row unless there is an existing row that matches on a unique index, in which case we replace it.
| operator bool ()
| Return true if the last query was successful.
bool | operator! ()
| Return true if the last query failed.

## Public Attributes

SQLQueryParms | def
| The default template parameters.

## Detailed Description

A class for building and executing SQL queries.

This class is derived from SQLQuery. It adds to that a tie between the query object and a MySQL++ Connection object, so that the query can be sent to the MySQL server we're connected to.

One does not generally create Query objects directly. Instead, call mysqlpp::Connection::query() to get one tied to that connection.

There are several ways to build and execute SQL queries with this class.

The way most like other database libraries is to pass a SQL statement to one of the exec*(), store*(), or use() methods taking a C or C++ string. The query is executed immediately, and any results returned.

For more complicated queries, you can use Query's stream interface. You simply build up a query using the Query instance as you would any other C++ stream object. When the query string is complete, you call the overloaded version of `exec*()`, `store*()` or `use()` that takes no parameters, which executes the built query and returns any results.

If you are using the library's Specialized SQL Structures feature, Query has several special functions for generating common SQL queries from those structures. For instance, it offers the insert() method, which builds an INSERT query to add the contents of the SSQLS to the database. As with the stream interface, these methods only build the query string; call one of the parameterless methods mentioned previously to actually execute the query.

Finally, you can build "template queries". This is something like C's `printf()` function, in that you insert a specially-formatted query string into the object which contains placeholders for data. You call the parse() method to tell the Query object that the query string contains placeholders. Once that's done, you can call any of the many overloaded methods that take a number of SQLStrings (up to 12 at the moment) or any type that can be converted to SQLString, and those parameters will be inserted into the placeholders. When you call one of the parameterless functions the execute the query, the final query string is assembled and sent to the server.

See the user manual for more details about these options.

## Constructor & Destructor Documentation

mysqlpp::Query::Query | ( | Connection * | c,
|  | bool | te = true
| ) | `[inline]`

Create a new query object attached to a connection.

This is the constructor used by mysqlpp::Connection::query().

Parameters:

  c | connection the finished query should be sent out on
  te | if true, throw exceptions on errors

mysqlpp::Query::Query | ( | const Query & | q | ) |

| Create a new query object as a copy of another. This is not a traditional copy ctor! Its only purpose is to make it possible to assign the return of Connection::query() to an empty Query object. In particular, the stream buffer and template query stuff will be empty in the copy, regardless of what values they have in the original.

## Member Function Documentation

std::string mysqlpp::Query::error | ( |  | ) |

| Get the last error message that was set. This class has an internal error message string, but if it isn't set, we return the last error message that happened on the connection we're bound to instead.

bool mysqlpp::Query::exec | ( | const std::string & | str | ) |

Execute a query.

Same as execute(), except that it only returns a flag indicating whether the query succeeded or not. It is basically a thin wrapper around the C API function `mysql_real_query()`.

Parameters:

  str | the query to execute

Returns:
  true if query was executed successfully

See also:
  execute(), store(), storein(), and use()

ResNSel mysqlpp::Query::execute | ( | const char * | str | ) |

| Execute query in a C++ string. Executes the query immediately, and returns the results.

ResNSel mysqlpp::Query::execute | ( |  | ) | `[inline]`

Execute built-up query.

Use one of the execute() overloads if you don't expect the server to return a result set. For instance, a DELETE query. The returned ResNSel object contains status information from the server, such as whether the query succeeded, and if so how many rows were affected.

This overloaded version of execute() simply executes the query that you have built up in the object in some way. (For instance, via the insert() method, or by using the object's stream interface.)

Returns:
  ResNSel status information about the query

See also:
  exec(), store(), storein(), and use()

template<class Iter>
Query& mysqlpp::Query::insert | ( | Iter | first,
|  | Iter | last
| ) | `[inline]`

Insert multiple new rows.

Builds an INSERT SQL query using items from a range within an STL container. Insert the entire contents of the container by using the begin() and end() iterators of the container as parameters to this function.

Parameters:

  first | iterator pointing to first element in range to insert
  last | iterator pointing to one past the last element to insert

See also:
  replace(), update()

template<class T>
Query& mysqlpp::Query::insert | ( | const T & | v | ) | `[inline]`

Insert a new row.

This function builds an INSERT SQL query. One uses it with MySQL++'s Specialized SQL Structures mechanism.

Parameters:

  v | new row

See also:
  replace(), update()

bool mysqlpp::Query::more_results | ( |  | ) |

Return whether more results are waiting for a multi-query or stored procedure response.

If this function returns true, you must call store_next() to fetch the next result set before you can execute more queries.

Wraps mysql_more_results() in the MySQL C API. That function only exists in MySQL v4.1 and higher. Therefore, this function always returns false when built against older API libraries.

Returns:
  true if another result set exists

Query & mysqlpp::Query::operator= | ( | const Query & | rhs | ) |

| Assign another query's state to this object. The same caveats apply to this operator as apply to the copy ctor.

void mysqlpp::Query::parse | ( |  | ) |

| Treat the contents of the query string as a template query. This method sets up the internal structures used by all of the other members that accept template query parameters. See the "Template Queries" chapter in the user manual for more information.

template<class T>
Query& mysqlpp::Query::replace | ( | const T & | v | ) | `[inline]`

Insert new row unless there is an existing row that matches on a unique index, in which case we replace it.

This function builds a REPLACE SQL query. One uses it with MySQL++'s Specialized SQL Structures mechanism.

Parameters:

  v | new row

See also:
  insert(), update()

void mysqlpp::Query::reset | ( |  | ) |

| Reset the query object so that it can be reused. This erases the query string and the contents of the parameterized query element list.

Result mysqlpp::Query::store | ( | const char * | str | ) |

| Execute query in a C++ string. Executes the query immediately, and returns an object that contains the entire result set. This is less memory-efficient than use(), but it lets you have random access to the results.

Result mysqlpp::Query::store | ( |  | ) | `[inline]`

Execute a query that can return a result set.

Use one of the store() overloads to execute a query and retrieve the entire result set into memory. This is useful if you actually need all of the records at once, but if not, consider using one of the use() methods instead, which returns the results one at a time, so they don't allocate as much memory as store().

You must use store(), storein() or use() for `SELECT`, `SHOW`, `DESCRIBE` and `EXPLAIN` queries. You can use these functions with other query types, but since they don't return a result set, exec() and execute() are more efficient.

The name of this method comes from the MySQL C API function it is implemented in terms of, `mysql_store_result()`.

This function has the same set of overloads as execute().

Returns:
  Result object containing entire result set

See also:
  exec(), execute(), storein(), and use()

Result mysqlpp::Query::store_next | ( |  | ) |

Return next result set, when processing a multi-query.

There are two cases where you'd use this function instead of the regular store() functions.

First, when handling the result of executing multiple queries at once. (See this page in the MySQL documentation for details.)

Second, when calling a stored procedure, MySQL can return the result as a set of results.

In either case, you must consume all results before making another MySQL query, even if you don't care about the remaining results or result sets.

As the MySQL documentation points out, you must set the MYSQL_OPTION_MULTI_STATEMENTS_ON flag on the connection in order to use this feature. See Connection::set_option().

Multi-queries only exist in MySQL v4.1 and higher. Therefore, this function just wraps store() when built against older API libraries.

Returns:
  Result object containing the next result set.

template<class Container>
void mysqlpp::Query::storein | ( | Container & | con,
|  | query_reset | r = RESET_QUERY
| ) | `[inline]`

Execute a query, and store the entire result set in an STL container.

This is a set of specialized template functions that call either storein_sequence() or storein_set(), depending on the type of container you pass it. It understands `std::vector`, `deque`, `list`, `slist` (a common C++ library extension), `set`, and `multiset`.

Like the functions it wraps, this is actually an overloaded set of functions. See the other functions' documentation for details.

Use this function if you think you might someday switch your program from using a set-associative container to a sequence container for storing result sets, or vice versa.

See exec(), execute(), store(), and use() for alternative query execution mechanisms.

template<class Sequence>
void mysqlpp::Query::storein_sequence | ( | Sequence & | con,
|  | query_reset | r = RESET_QUERY
| ) | `[inline]`

Execute a query, storing the result set in an STL sequence container.

This function works much like store() from the caller's perspective, because it returns the entire result set at once. It's actually implemented in terms of use(), however, so that memory for the result set doesn't need to be allocated twice.

There are many overloads for this function, pretty much the same as for execute(), except that there is a Container parameter at the front of the list. So, you can pass a container and a query string, or a container and template query parameters.

Parameters:

  con | any STL sequence container, such as `std::vector`
  r | whether the query automatically resets after being used

See also:
  exec(), execute(), store(), and use()

template<class Set>
void mysqlpp::Query::storein_set | ( | Set & | con,
|  | query_reset | r = RESET_QUERY
| ) | `[inline]`

| Execute a query, storing the result set in an STL associative container. The same thing as storein_sequence(), except that it's used with associative STL containers, such as `std::set`. Other than that detail, that method's comments apply equally well to this one.

std::string mysqlpp::Query::str | ( | SQLQueryParms & | p,
|  | query_reset | r
| ) |

Get built query as a null-terminated C++ string.

Parameters:

  p | template query parameters to use, overriding the ones this object holds, if any
  r | if equal to `RESET_QUERY`, query object is cleared after this call

std::string mysqlpp::Query::str | ( | SQLQueryParms & | p | ) |

Get built query as a null-terminated C++ string.

Parameters:

  p | template query parameters to use, overriding the ones this object holds, if any

std::string mysqlpp::Query::str | ( | query_reset | r | ) | `[inline]`

Get built query as a null-terminated C++ string.

Parameters:

  r | if equal to `RESET_QUERY`, query object is cleared after this call

bool mysqlpp::Query::success | ( |  | ) |

| Returns true if the last operation succeeded. Returns true if the last query succeeded, and the associated Connection object's success() method also returns true. If either object is unhappy, this method returns false.

template<class T>
Query& mysqlpp::Query::update | ( | const T & | o,
|  | const T & | n
| ) | `[inline]`

Replace an existing row's data with new data.

This function builds an UPDATE SQL query using the new row data for the SET clause, and the old row data for the WHERE clause. One uses it with MySQL++'s Specialized SQL Structures mechanism.

Parameters:

  o | old row
  n | new row

See also:
  insert(), replace()

ResUse mysqlpp::Query::use | ( | const char * | str | ) |

| Execute query in a C++ string. Executes the query immediately, and returns an object that lets you walk through the result set one row at a time, in sequence. This is more memory-efficient than store().

ResUse mysqlpp::Query::use | ( |  | ) | `[inline]`

Execute a query that can return a result set.

Use one of the use() overloads if memory efficiency is important. They return an object that can walk through the result records one by one, without fetching the entire result set from the server. This is superior to store() when there are a large number of results; store() would have to allocate a large block of memory to hold all those records, which could cause problems.

A potential downside of this method is that MySQL database resources are tied up until the result set is completely consumed. Do your best to walk through the result set as expeditiously as possible.

The name of this method comes from the MySQL C API function that initiates the retrieval process, `mysql_use_result()`. This method is implemented in terms of that function.

This function has the same set of overloads as execute().

Returns:
  ResUse object that can walk through result set serially

See also:
  exec(), execute(), store() and storein()

## Member Data Documentation

SQLQueryParms mysqlpp::Query::def

| The default template parameters. Used for filling in parameterized queries.

The documentation for this class was generated from the following files:

- query.h
- query.cpp