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Robert Adam
158 lines
7.5 KiB
Markdown
158 lines
7.5 KiB
Markdown
# PostgreSQL Backend Reference
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SOCI backend for accessing PostgreSQL database.
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## Prerequisites
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### Supported Versions
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The SOCI PostgreSQL backend is supported for use with PostgreSQL >= 9.0, although older versions may suffer from limited feature support. See below for details.
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### Tested Platforms
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|PostgreSQL|OS|Compiler|
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|--- |--- |--- |
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| 14|macOS 11.7|AppleClang 13|
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| 14|Ubuntu 22.04|gcc 11.4|
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| 13|Windows Server 2019|MSVS 2022|
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| 12|Windows Server 2019|MSVS 2019|
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| 11|Windows Server 2016|MSVS 2017|
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| 10|Windows Server 2012 R2|MSVS 2015|
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|9.4|Windows Server 2012 R2|Mingw-w64/GCC 8.1|
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### Required Client Libraries
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The SOCI PostgreSQL backend requires PostgreSQL's `libpq` client library.
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Note that the SOCI library itself depends also on `libdl`, so the minimum set of libraries needed to compile a basic client program is:
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```console
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-lsoci_core -lsoci_postgresql -ldl -lpq
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```
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### Connecting to the Database
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To establish a connection to the PostgreSQL database, create a `session` object using the `postgresql` backend factory together with a connection string:
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```cpp
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session sql(postgresql, "dbname=mydatabase");
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// or:
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session sql("postgresql", "dbname=mydatabase");
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// or:
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session sql("postgresql://dbname=mydatabase");
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```
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The set of parameters used in the connection string for PostgreSQL is the same as accepted by the [PQconnectdb](https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-PQCONNECTDB) function from the `libpq` library.
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In addition to standard PostgreSQL connection parameters, the following can be set:
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* `singlerow` or `singlerows`
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For example:
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```cpp
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session sql(postgresql, "dbname=mydatabase singlerows=true");
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```
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If the `singlerows` parameter is set to `true` or `yes`, then queries will be executed in the single-row mode, which prevents the client library from loading full query result sets into memory and instead fetches rows one by one, as they are requested by the statement's fetch() function. This mode can be of interest to those users who want to make their client applications more responsive (with more fine-grained operation) by avoiding potentially long blocking times when complete query results are loaded to client's memory.
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Note that in the single-row operation:
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* bulk queries are not supported, and
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* in order to fulfill the expectations of the underlying client library, the complete rowset has to be exhausted before executing further queries on the same session.
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Once you have created a `session` object as shown above, you can use it to access the database, for example:
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```cpp
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int count;
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sql << "select count(*) from invoices", into(count);
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```
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(See the [connection](../connections.md) and [data binding](../binding.md) documentation for general information on using the `session` class.)
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## SOCI Feature Support
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### Dynamic Binding
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The PostgreSQL backend supports the use of the SOCI `row` class, which facilitates retrieval of data whose type is not known at compile time.
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When calling `row::get<T>()`, the type you should pass as `T` depends upon the underlying database type. For the PostgreSQL backend, this type mapping is:
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| PostgreSQL Data Type | SOCI Data Type (`data_type`) | `row::get<T>` specializations |
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| ------------------------------------------------------------ | ---------------------------- | ----------------------------- |
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| numeric, real, double | dt_double | double |
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| boolean, smallint, integer | dt_integer | int |
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| int8 | dt_long_long | long long |
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| oid | dt_integer | unsigned long |
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| char, varchar, text, cstring, bpchar | dt_string | std::string |
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| abstime, reltime, date, time, timestamp, timestamptz, timetz | dt_date | std::tm |
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| PostgreSQL Data Type | SOCI Data Type (`db_type`) | `row::get<T>` specializations |
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| ------------------------------------------------------------ | ---------------------------- | ----------------------------- |
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| numeric, real, double | db_double | double |
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| boolean | db_int8 | int8_t |
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| smallint | db_int16 | int16_t |
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| integer | db_int32 | int32_t |
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| int8 | db_int64 | int64_t |
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| oid | db_int32 | int32_t |
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| char, varchar, text, cstring, bpchar | db_string | std::string |
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| abstime, reltime, date, time, timestamp, timestamptz, timetz | db_date | std::tm |
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(See the [dynamic resultset binding](../types.md#dynamic-binding) documentation for general information on using the `row` class.)
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### Binding by Name
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In addition to [binding by position](../binding.md#binding-by-position), the PostgreSQL backend supports [binding by name](../binding.md#binding-by-name), via an overload of the `use()` function:
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```cpp
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int id = 7;
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sql << "select name from person where id = :id", use(id, "id")
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```
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### Bulk Operations
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The PostgreSQL backend has full support for SOCI's [bulk operations](../binding.md#bulk-operations) interface.
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### Transactions
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[Transactions](../transactions.md) are also fully supported by the PostgreSQL backend.
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### blob Data Type
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The PostgreSQL backend supports working with data stored in columns of type Blob, via SOCI's [blob](../lobs.md) class.
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Note that 64-bit offsets require PostgreSQL client library 9.3 or later.
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### rowid Data Type
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The concept of row identifier (OID in PostgreSQL) is supported via SOCI's [rowid](../api/client.md#class-rowid) class.
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### Nested Statements
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Nested statements are not supported by PostgreSQL backend.
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### Stored Procedures
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PostgreSQL stored procedures can be executed by using SOCI's [procedure](../procedures.md) class.
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## Native API Access
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SOCI provides access to underlying database APIs via several `get_backend()` functions, as described in the [beyond SOCI](../beyond.md) documentation.
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The PostgreSQL backend provides the following concrete classes for native API access:
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|Accessor Function|Concrete Class|
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|--- |--- |
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|session_backend * session::get_backend()|postgresql_session_backend|
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|statement_backend * statement::get_backend()|postgresql_statement_backend|
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|blob_backend * blob::get_backend()|postgresql_blob_backend|
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|rowid_backend * rowid::get_backend()|postgresql_rowid_backend|
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## Backend-specific extensions
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### uuid Data Type
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The PostgreSQL backend supports working with data stored in columns of type UUID via simple string operations. All string representations of UUID supported by PostgreSQL are accepted on input, the backend will return the standard
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format of UUID on output. See the test `test_uuid_column_type_support` for usage examples.
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