Struct odbc_api::Connection

pub struct Connection<'c> { /* fields omitted */ }

The connection handle references storage of all information about the connection to the data source, including status, transaction state, and error information.

Implementations

impl<'c> Connection<'c>

pub fn execute_utf16(
    &self,
    query: &U16Str,
    params: impl ParameterCollection
) -> Result<Option<CursorImpl<'_, Statement<'_>>>, Error>

Executes an sql statement using a wide string. See Self::execute.

pub fn execute(
    &self,
    query: &str,
    params: impl ParameterCollection
) -> Result<Option<CursorImpl<'_, Statement<'_>>>, Error>

Executes an SQL statement. This is the fastest way to submit an SQL statement for one-time execution.

Parameters

• query: The text representation of the SQL statement. E.g. "SELECT * FROM my_table;".
• params: ? may be used as a placeholder in the statement text. You can use () to represent no parameters. See the crate::parameter module level documentation for more information on how to pass parameters.

Return

Returns Some if a cursor is created. If None is returned no cursor has been created ( e.g. the query came back empty). Note that an empty query may also create a cursor with zero rows.

Example

use odbc_api::Environment;

// I herby solemnly swear that this is the only ODBC environment in the entire process, thus
// making this call safe.
let env = unsafe {
    Environment::new()?
};

let mut conn = env.connect("YourDatabase", "SA", "<YourStrong@Passw0rd>")?;
if let Some(cursor) = conn.execute("SELECT year, name FROM Birthdays;", ())? {
    // Use cursor to process query results.  
}

pub fn prepare_utf16(&self, query: &U16Str) -> Result<Prepared<'_>, Error>

Prepares an SQL statement. This is recommended for repeated execution of similar queries.

Parameters

• query: The text representation of the SQL statement. E.g. "SELECT * FROM my_table;". ? may be used as a placeholder in the statement text, to be replaced with parameters during execution.

pub fn prepare(&self, query: &str) -> Result<Prepared<'_>, Error>

Prepares an SQL statement. This is recommended for repeated execution of similar queries.

Parameters

• query: The text representation of the SQL statement. E.g. "SELECT * FROM my_table;". ? may be used as a placeholder in the statement text, to be replaced with parameters during execution.

pub fn preallocate(&self) -> Result<Preallocated<'_>, Error>

Allocates an SQL statement handle. This is recommended if you want to sequentially execute different queries over the same connection, as you avoid the overhead of allocating a statement handle for each query.

Should you want to repeatedly execute the same query with different parameters try Self::prepare instead.

Example

use odbc_api::{Connection, Error};
use std::io::{self, stdin, Read};

fn interactive(conn: &Connection) -> io::Result<()>{
    let mut statement = conn.preallocate().unwrap();
    let mut query = String::new();
    stdin().read_line(&mut query)?;
    while !query.is_empty() {
        match statement.execute(&query, ()) {
            Err(e) => println!("{}", e),
            Ok(None) => println!("No results set generated."),
            Ok(Some(cursor)) => {
                // ...print cursor contents...
            },
        }
        stdin().read_line(&mut query)?;
    }
    Ok(())
}

pub fn set_autocommit(&self, enabled: bool) -> Result<(), Error>

Specify the transaction mode. By default, ODBC transactions are in auto-commit mode. Switching from manual-commit mode to auto-commit mode automatically commits any open transaction on the connection. There is no open or begin transaction method. Each statement execution automatically starts a new transaction or adds to the existing one.

In manual commit mode you can use Connection::commit or Connection::rollback. Keep in mind, that even SELECT statements can open new transactions. This library will rollback open transactions if a connection goes out of SCOPE. This however will log an error, since the transaction state is only discovered during a failed disconnect. It is preferable that the appliacation makes sure all transactions are closed if in manual commit mode.

pub fn commit(&self) -> Result<(), Error>

To commit a transaction in manual-commit mode.

pub fn rollback(&self) -> Result<(), Error>

To rollback a transaction in manual-commit mode.

pub unsafe fn promote_to_send(self) -> Send<Self>

Allows sending this connection to different threads. This Connection will still be only be used by one thread at a time, but it may be a different thread each time.

Example

use std::thread;
use lazy_static::lazy_static;
use odbc_api::Environment;
lazy_static! {
    static ref ENV: Environment = unsafe { Environment::new().unwrap() };
}
const MSSQL: &str =
    "Driver={ODBC Driver 17 for SQL Server};\
    Server=localhost;\
    UID=SA;\
    PWD=<YourStrong@Passw0rd>;\
";

let conn = ENV.connect_with_connection_string("MSSQL").unwrap();
let conn = unsafe { conn.promote_to_send() };
let handle = thread::spawn(move || {
    if let Some(cursor) = conn.execute("SELECT title FROM Movies ORDER BY year",())? {
        // Use cursor to process results
    }
    Ok::<(), odbc_api::Error>(())
});
handle.join().unwrap()?;

Safety

According to the ODBC standard this should be safe. By calling this function you express your trust in the implementation of the ODBC driver your application is using.

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

This function may be removed in future versions of this crate and connections would be Send and Sync out of the Box. This will require sufficient testing in which a wide variety of database drivers prove to be thread safe. For now this API tries to error on the side of caution, and leaves the amount of trust you want to put in the driver implementation to the user. I have seen this go wrong in the past, but time certainly improved the situation. At one point this will be cargo cult and Connection can be Send and Sync by default (hopefully).

Note to users of unixodbc: You may configure the threading level to make unixodbc synchronize access to the driver (and therby making them thread safe if they are not thread safe by themself. This may however hurt your performancy if the driver would actually be able to perform operations in parallel.

See: https://stackoverflow.com/questions/4207458/using-unixodbc-in-a-multithreaded-concurrent-setting

Trait Implementations

impl<'conn> Drop for Connection<'conn>

fn drop(&mut self)

Executes the destructor for this type.