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Günter Obiltschnig 2021-06-24 22:15:04 +02:00
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@ -5,8 +5,9 @@ POCO Data Library
POCO Data is POCO's database abstraction layer which allows users to POCO Data is POCO's database abstraction layer which allows users to
easily send/retrieve data to/from various databases. Currently supported easily send/retrieve data to/from various databases. Currently supported
database connectors are SQLite, MySQL and ODBC. Framework is opened database connectors are SQLite, MySQL/MariaDB, PostgreSQL and ODBC (which
for extension, so additional native connectors (Oracle, PostgreSQL, ...) covers SQL Server and other databases).
Framework is opened for extension, so additional native connectors (Oracle, Db2, ...)
can be added. The intent behind the Poco::Data framework is to produce the can be added. The intent behind the Poco::Data framework is to produce the
integration between C++ and relational databses in a simple and natural way. integration between C++ and relational databses in a simple and natural way.
@ -123,7 +124,10 @@ a complete ODBC driver-specific connection string defining all the necessary con
For MySQL, the connection string is a semicolon-delimited list of name-value pairs For MySQL, the connection string is a semicolon-delimited list of name-value pairs
specifying various parameters like host, port, user, password, database, compression and specifying various parameters like host, port, user, password, database, compression and
automatic reconnect. Example: <["host=localhost;port=3306;db=mydb;user=alice;password=s3cr3t;compress=true;auto-reconnect=true"]> automatic reconnect. Example:
"host=localhost;port=3306;db=mydb;user=alice;password=s3cr3t;compress=true;auto-reconnect=true"
----
!!!Inserting and Retrieving Data !!!Inserting and Retrieving Data
@ -139,17 +143,17 @@ Assume we have a table that stores only forenames:
If we want to insert one single forename we could simply write: If we want to insert one single forename we could simply write:
std::string aName("Peter"); std::string aName("Peter");
session << "INSERT INTO FORENAME VALUES(" << aName << ")", now; session << "INSERT INTO FORENAME VALUES('" << aName << "')", now;
---- ----
However, a better solution is to use <*placeholders*> and connect each However, a better solution is to use <*placeholders*> and connect each
placeholder via a <[use]> expression with a variable that will provide placeholder via a `use` expression with a variable that will provide
the value during execution. Placeholders, depending on your database are the value during execution. Placeholders, depending on your database are
recognized by having either a colon(<[:]>) in front of the name or recognized by having either a colon (`:`) in front of the name or
simply by a question mark (<[?]>) as a placeholder. While having the simply by a question mark (`?`) as a placeholder. While having the
placeholders marked with a colon followed by a human-readable name is placeholders marked with a colon followed by a human-readable name is
very convenient due to readability, not all SQL dialects support this and very convenient due to readability, not all SQL dialects support this and
universally accepted standard placeholder is (<[?]>). Consult your database universally accepted standard placeholder is `?`. Consult your database
SQL documentation to determine the valid placeholder syntax. SQL documentation to determine the valid placeholder syntax.
Rewriting the above code now simply gives: Rewriting the above code now simply gives:
@ -609,8 +613,8 @@ not!> be used in conjunction with <[out]> and <[io]> under any
circumstances: <[std::vector<bool>]> . The details are beyond the scope circumstances: <[std::vector<bool>]> . The details are beyond the scope
of this manual. For those interested to learn more about it, there is an of this manual. For those interested to learn more about it, there is an
excellent explanation in S. Meyers book "Efective STL", Item 18 or Gotw excellent explanation in S. Meyers book "Efective STL", Item 18 or Gotw
#50, [[http://www.gotw.ca/gotw/050.htm When Is a Container Not a #50, [[http://www.gotw.ca/gotw/050.htm When Is a Container Not a Container]]
Container]] paragraph. paragraph.
!!!Tuples !!!Tuples
@ -771,8 +775,8 @@ size of data set we want to fetch, either explicitly as in the code
above or implicitly, through size of the supplied container as in above or implicitly, through size of the supplied container as in
following example: following example:
std::vector<int> ints(100, 1); std::vector<int> ints(100, 1);
session << "SELECT * FROM Test", into(ints, bulk), now; session << "SELECT * FROM Test", into(ints, bulk), now;
---- ----
For statements that generate their ow internal extraction storage (see For statements that generate their ow internal extraction storage (see