Struct Connection

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

Expand description

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

If you want to enable the connection pooling support build into the ODBC driver manager have a look at crate::Environment::set_connection_pooling.

Implementations§

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impl<'c> Connection<'c>

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pub fn into_sys(self) -> HDbc

Transfers ownership of the handle to this open connection to the raw ODBC pointer.

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pub fn into_handle(self) -> Connection<'c>

Transfer ownership of this open connection to a wrapper around the raw ODBC pointer. The wrapper allows you to call ODBC functions on the handle, but doesn’t care if the connection is in the right state.

You should not have a need to call this method if your use case is covered by this library, but, in case it is not, this may help you to break out of the type structure which might be to rigid for you, while simultaneously abondoning its safeguards.

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pub fn execute( &self, query: &str, params: impl ParameterCollectionRef, ) -> Result<Option<CursorImpl<StatementImpl<'_>>>, 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, ConnectionOptions};

let env = Environment::new()?;

let mut conn = env.connect(
    "YourDatabase", "SA", "My@Test@Password1",
    ConnectionOptions::default()
)?;
if let Some(cursor) = conn.execute("SELECT year, name FROM Birthdays;", ())? {
    // Use cursor to process query results.  
}

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pub async fn execute_polling( &self, query: &str, params: impl ParameterCollectionRef, sleep: impl Sleep, ) -> Result<Option<CursorPolling<StatementImpl<'_>>>, Error>

Asynchronous sibling of Self::execute. Uses polling mode to be asynchronous. sleep does govern the behaviour of polling, by waiting for the future in between polling. Sleep should not be implemented using a sleep which blocks the system thread, but rather utilize the methods provided by your async runtime. E.g.:

use odbc_api::{Connection, IntoParameter, Error};
use std::time::Duration;

async fn insert_post<'a>(
    connection: &'a Connection<'a>,
    user: &str,
    post: &str,
) -> Result<(), Error> {
    // Poll every 50 ms.
    let sleep = || tokio::time::sleep(Duration::from_millis(50));
    let sql = "INSERT INTO POSTS (user, post) VALUES (?, ?)";
    // Execute query using ODBC polling method
    let params = (&user.into_parameter(), &post.into_parameter());
    connection.execute_polling(&sql, params, sleep).await?;
    Ok(())
}

Attention: This feature requires driver support, otherwise the calls will just block until they are finished. At the time of writing this out of Microsoft SQL Server, PostgerSQL, SQLite and MariaDB this worked only with Microsoft SQL Server. For code generic over every driver you may still use this. The functions will return with the correct results just be aware that may block until they are finished.

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pub fn into_cursor( self, query: &str, params: impl ParameterCollectionRef, ) -> Result<Option<CursorImpl<StatementConnection<'c>>>, ConnectionAndError<'c>>

In some use cases there you only execute a single statement, or the time to open a connection does not matter users may wish to choose to not keep a connection alive seperatly from the cursor, in order to have an easier time with the borrow checker.

use odbc_api::{environment, Error, Cursor, ConnectionOptions};


const CONNECTION_STRING: &str =
    "Driver={ODBC Driver 18 for SQL Server};\
    Server=localhost;UID=SA;\
    PWD=My@Test@Password1;";

fn execute_query(query: &str) -> Result<Option<impl Cursor>, Error> {
    let env = environment()?;
    let conn = env.connect_with_connection_string(
        CONNECTION_STRING,
        ConnectionOptions::default()
    )?;

    // connect.execute(&query, ()) // Compiler error: Would return local ref to `conn`.

    let maybe_cursor = conn.into_cursor(&query, ())?;
    Ok(maybe_cursor)
}

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

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

Should your use case require you to execute the same query several times with different parameters, prepared queries are the way to go. These give the database a chance to cache the access plan associated with your SQL statement. It is not unlike compiling your program once and executing it several times.

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

fn interactive(conn: &Connection) -> io::Result<()>{
    let mut prepared = conn.prepare("SELECT * FROM Movies WHERE title=?;").unwrap();
    let mut title = String::new();
    stdin().read_line(&mut title)?;
    while !title.is_empty() {
        match prepared.execute(&title.as_str().into_parameter()) {
            Err(e) => println!("{}", e),
            // Most drivers would return a result set even if no Movie with the title is found,
            // the result set would just be empty. Well, most drivers.
            Ok(None) => println!("No result set generated."),
            Ok(Some(cursor)) => {
                // ...print cursor contents...
            }
        }
        stdin().read_line(&mut title)?;
    }
    Ok(())
}

§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.

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pub fn into_prepared( self, query: &str, ) -> Result<Prepared<StatementConnection<'c>>, Error>

Prepares an SQL statement which takes ownership of the connection. The advantage over Self::prepare is, that you do not need to keep track of the lifetime of the connection seperatly and can create types which do own the prepared query and only depend on the lifetime of the environment. The downside is that you can not use the connection for anything else anymore.

§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.

use odbc_api::{
    environment, Error, ColumnarBulkInserter, StatementConnection,
    buffers::{BufferDesc, AnyBuffer}, ConnectionOptions
};

const CONNECTION_STRING: &str =
    "Driver={ODBC Driver 18 for SQL Server};\
    Server=localhost;UID=SA;\
    PWD=My@Test@Password1;";

/// Supports columnar bulk inserts on a heterogenous schema (columns have different types),
/// takes ownership of a connection created using an environment with static lifetime.
type Inserter = ColumnarBulkInserter<StatementConnection<'static>, AnyBuffer>;

/// Creates an inserter which can be reused to bulk insert birthyears with static lifetime.
fn make_inserter(query: &str) -> Result<Inserter, Error> {
    let env = environment()?;
    let conn = env.connect_with_connection_string(
        CONNECTION_STRING,
        ConnectionOptions::default()
    )?;
    let prepared = conn.into_prepared("INSERT INTO Birthyear (name, year) VALUES (?, ?)")?;
    let buffers = [
        BufferDesc::Text { max_str_len: 255},
        BufferDesc::I16 { nullable: false },
    ];
    let capacity = 400;
    prepared.into_column_inserter(capacity, buffers)
}

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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(())
}

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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 application makes sure all transactions are closed if in manual commit mode.

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

To commit a transaction in manual-commit mode.

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

To rollback a transaction in manual-commit mode.

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

Indicates the state of the connection. If true the connection has been lost. If false, the connection is still active.

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pub fn packet_size(&self) -> Result<u32, Error>

Network packet size in bytes. Requries driver support.

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

Get the name of the database management system used by the connection.

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pub fn max_catalog_name_len(&self) -> Result<u16, Error>

Maximum length of catalog names.

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pub fn max_schema_name_len(&self) -> Result<u16, Error>

Maximum length of schema names.

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pub fn max_table_name_len(&self) -> Result<u16, Error>

Maximum length of table names.

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pub fn max_column_name_len(&self) -> Result<u16, Error>

Maximum length of column names.

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

Get the name of the current catalog being used by the connection.

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pub fn columns( &self, catalog_name: &str, schema_name: &str, table_name: &str, column_name: &str, ) -> Result<CursorImpl<StatementImpl<'_>>, Error>

A cursor describing columns of all tables matching the patterns. Patterns support as placeholder % for multiple characters or _ for a single character. Use \ to escape.The returned cursor has the columns: TABLE_CAT, TABLE_SCHEM, TABLE_NAME, COLUMN_NAME, DATA_TYPE, TYPE_NAME, COLUMN_SIZE, BUFFER_LENGTH, DECIMAL_DIGITS, NUM_PREC_RADIX, NULLABLE, REMARKS, COLUMN_DEF, SQL_DATA_TYPE, SQL_DATETIME_SUB, CHAR_OCTET_LENGTH, ORDINAL_POSITION, IS_NULLABLE.

In addition to that there may be a number of columns specific to the data source.

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pub fn tables( &self, catalog_name: &str, schema_name: &str, table_name: &str, table_type: &str, ) -> Result<CursorImpl<StatementImpl<'_>>, Error>

List tables, schemas, views and catalogs of a datasource.

§Parameters

catalog_name: Filter result by catalog name. Accept search patterns. Use % to match any number of characters. Use _ to match exactly on character. Use \ to escape characeters.
schema_name: Filter result by schema. Accepts patterns in the same way as catalog_name.
table_name: Filter result by table. Accepts patterns in the same way as catalog_name.
table_type: Filters results by table type. E.g: ‘TABLE’, ‘VIEW’. This argument accepts a comma separeted list of table types. Omit it to not filter the result by table type at all.

§Example

use odbc_api::{Connection, Cursor, Error, ResultSetMetadata, buffers::TextRowSet};

fn print_all_tables(conn: &Connection<'_>) -> Result<(), Error> {
    // Set all filters to an empty string, to really print all tables
    let mut cursor = conn.tables("", "", "", "")?;

    // The column are gonna be TABLE_CAT,TABLE_SCHEM,TABLE_NAME,TABLE_TYPE,REMARKS, but may
    // also contain additional driver specific columns.
    for (index, name) in cursor.column_names()?.enumerate() {
        if index != 0 {
            print!(",")
        }
        print!("{}", name?);
    }

    let batch_size = 100;
    let mut buffer = TextRowSet::for_cursor(batch_size, &mut cursor, Some(4096))?;
    let mut row_set_cursor = cursor.bind_buffer(&mut buffer)?;

    while let Some(row_set) = row_set_cursor.fetch()? {
        for row_index in 0..row_set.num_rows() {
            if row_index != 0 {
                print!("\n");
            }
            for col_index in 0..row_set.num_cols() {
                if col_index != 0 {
                    print!(",");
                }
                let value = row_set
                    .at_as_str(col_index, row_index)
                    .unwrap()
                    .unwrap_or("NULL");
                print!("{}", value);
            }
        }
    }

    Ok(())
}

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pub fn foreign_keys( &self, pk_catalog_name: &str, pk_schema_name: &str, pk_table_name: &str, fk_catalog_name: &str, fk_schema_name: &str, fk_table_name: &str, ) -> Result<CursorImpl<StatementImpl<'_>>, Error>

This can be used to retrieve either a list of foreign keys in the specified table or a list of foreign keys in other table that refer to the primary key of the specified table.

See: https://learn.microsoft.com/en-us/sql/odbc/reference/syntax/sqlforeignkeys-function

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