Struct odbc_api::handles::Environment

pub struct Environment { /* fields omitted */ }

An Environment is a global context, in which to access data.

Associated with an Environment is any information that is global in nature, such as:

• The Environment’s state
• The current environment-level diagnostics
• The handles of connections currently allocated on the environment
• The current stetting of each environment attribute

Implementations

impl Environment

pub unsafe fn set_connection_pooling(
    scheme: AttrConnectionPooling
) -> Result<(), Error>

Enable or disable (default) connection pooling for ODBC connections. Call this function before creating the ODBC environment for which you want to enable connection pooling.

See: https://docs.microsoft.com/en-us/sql/odbc/reference/develop-app/driver-manager-connection-pooling

Safety

An ODBC driver must be fully thread-safe, and connections must not have thread affinity to support connection pooling. This means the driver is able to handle a call on any thread at any time and is able to connect on one thread, to use the connection on another thread, and to disconnect on a third thread.

pub fn set_connection_pooling_matching(
    &mut self,
    matching: AttrCpMatch
) -> Result<(), Error>

pub unsafe fn new() -> Result<Self, Error>

An allocated ODBC Environment handle

Safety

There may only be one Odbc environment in any process at any time. Take care using this function in unit tests, as these run in parallel by default in Rust. Also no library should probably wrap the creation of an odbc environment into a safe function call. This is because using two of these “safe” libraries at the same time in different parts of your program may lead to race condition thus violating Rust’s safety guarantees.

Creating one environment in your binary is safe however.

pub fn declare_version(&self, version: AttrOdbcVersion) -> Result<(), Error>

Declares which Version of the ODBC API we want to use. This is the first thing that should be done with any ODBC environment.

pub fn allocate_connection(&self) -> Result<Connection<'_>, Error>

Allocate a new connection handle. The Connection must not outlive the Environment.

pub fn as_raw(&self) -> HEnv

Provides access to the raw ODBC environment handle.

pub unsafe fn drivers_buffer_fill(
    &self,
    direction: FetchOrientation,
    buffer_description: &mut Vec<u16>,
    buffer_attributes: &mut Vec<u16>
) -> Result<bool, Error>

List drivers descriptions and driver attribute keywords.

Safety

Callers need to make sure only one thread is iterating over driver information at a time. Method changes environment state. This method would be safe to call via an exclusive &mut reference, yet that would restrict usecases. E.g. requesting information would only be possible before connections borrow a reference.

Parameters

• direction: Determines whether the Driver Manager fetches the next driver in the list (FetchOrientation::Next) or whether the search starts from the beginning of the list (FetchOrientation::First).
• buffer_description: In case true is returned this buffer is filled with the description of the driver.
• buffer_attributes: In case true is returned this buffer is filled with a list of key value attributes. E.g.: "key1=value1\0key2=value2\0\0".

Use Environment::drivers_buffer_len to determine buffer lengths.

See SQLDrivers

pub unsafe fn drivers_buffer_len(
    &self,
    direction: FetchOrientation
) -> Result<Option<(i16, i16)>, Error>

Use together with Environment::drivers_buffer_fill to list drivers descriptions and driver attribute keywords.

Safety

Callers need to make sure only one thread is iterating over driver information at a time. Method changes environment state. This method would be safe to call via an exclusive &mut reference, yet that would restrict usecases. E.g. requesting information would only be possible before connections borrow a reference.

Parameters

• direction: Determines whether the Driver Manager fetches the next driver in the list (FetchOrientation::Next) or whether the search starts from the beginning of the list (FetchOrientation::First).

Return

(driver description length, attribute length). Length is in characters minus terminating terminating zero.

See SQLDrivers

pub unsafe fn data_source_buffer_len(
    &self,
    direction: FetchOrientation
) -> Result<Option<(i16, i16)>, Error>

Use together with Environment::data_source_buffer_fill to list drivers descriptions and driver attribute keywords.

Safety

Callers need to make sure only one thread is iterating over data source information at a time. Method changes environment state. This method would be safe to call via an exclusive &mut reference, yet that would restrict usecases. E.g. requesting information would only be possible before connections borrow a reference.

Parameters

• direction: Determines whether the Driver Manager fetches the next driver in the list (FetchOrientation::Next) or whether the search starts from the beginning of the list (FetchOrientation::First, FetchOrientation::FirstSystem, FetchOrientation::FirstUser).

Return

(server name length, description length). Length is in characters minus terminating zero.

pub unsafe fn data_source_buffer_fill(
    &self,
    direction: FetchOrientation,
    buffer_name: &mut Vec<u16>,
    buffer_description: &mut Vec<u16>
) -> Result<bool, Error>

List drivers descriptions and driver attribute keywords.

Safety

Callers need to make sure only one thread is iterating over data source information at a time. Method changes environment state. This method would be safe to call via an exclusive &mut reference, yet that would restrict usecases. E.g. requesting information would only be possible before connections borrow a reference.

Parameters

• direction: Determines whether the Driver Manager fetches the next driver in the list (FetchOrientation::Next) or whether the search starts from the beginning of the list (FetchOrientation::First, FetchOrientation::FirstSystem, FetchOrientation::FirstUser).
• buffer_name: In case true is returned this buffer is filled with the name of the datasource.
• buffer_description: In case true is returned this buffer is filled with a description of the datasource (i.e. Driver name).

Use Environment::data_source_buffer_len to determine buffer lengths.

Trait Implementations

impl AsHandle for Environment

fn as_handle(&self) -> Handle

The raw underlying ODBC handle used to talk to the ODBC C API. The handle must be valid.

fn handle_type(&self) -> HandleType

The type of the ODBC handle returned by as_handle.

impl Debug for Environment

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Drop for Environment

fn drop(&mut self)

Executes the destructor for this type.

impl Send for Environment

See: https://docs.microsoft.com/en-us/sql/odbc/reference/develop-app/multithreading?view=sql-server-ver15

impl Sync for Environment

See: https://docs.microsoft.com/en-us/sql/odbc/reference/develop-app/multithreading?view=sql-server-ver15