Struct Preallocated

pub struct Preallocated<'open_connection> { /* private fields */ }

A preallocated SQL statement handle intended for sequential execution of different queries. See crate::Connection::preallocate.

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(())
}

Implementations

impl<'o> Preallocated<'o>

pub unsafe fn new(statement: StatementImpl<'o>) -> Self

Users which intend to write their application in safe Rust should prefer using crate::Connection::preallocate as opposed to this constructor.

Safety

statement must be an allocated handled with no pointers bound for either results or arguments. The statement must not be prepared, but in the state of a “freshly” allocated handle.

pub fn execute( &mut self, query: &str, params: impl ParameterCollectionRef, ) -> Result<Option<CursorImpl<&mut StatementImpl<'o>>>, Error>

Executes a statement. This is the fastest way to sequentially execute different SQL Statements.

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. Check 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. Since we want to reuse the statement handle a returned cursor will not take ownership of it and instead borrow it.

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 into_statement(self) -> StatementImpl<'o>

Transfer ownership to the underlying statement handle.

The resulting type is one level of indirection away from the raw pointer of the ODBC API. It no longer has any guarantees about bound buffers, but is still guaranteed to be a valid allocated statement handle. This serves together with crate::handles::StatementImpl::into_sys or crate::handles::Statement::as_sys this serves as an escape hatch to access the functionality provided by crate::sys not yet accessible through safe abstractions.

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

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

pub fn foreign_keys( &mut 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<&mut StatementImpl<'o>>, 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

pub fn row_count(&mut self) -> Result<Option<usize>, Error>

Number of rows affected by the last INSERT, UPDATE or DELETE statment. May return None if row count is not available. Some drivers may also allow to use this to determine how many rows have been fetched using SELECT. Most drivers however only know how many rows have been fetched after they have been fetched.

use odbc_api::{Connection, Error};

/// Make everyone rich and return how many colleagues are happy now.
fn raise_minimum_salary(
    conn: &Connection<'_>,
    new_min_salary: i32
) -> Result<usize, Error> {
    // We won't use conn.execute directly, because we need a handle to ask about the number
    // of changed rows. So let's allocate the statement explicitly.
    let mut stmt = conn.preallocate()?;
    stmt.execute(
        "UPDATE Employees SET salary = ? WHERE salary < ?",
        (&new_min_salary, &new_min_salary),
    )?;
    let number_of_updated_rows = stmt
        .row_count()?
        .expect("For UPDATE statements row count must always be available.");
    Ok(number_of_updated_rows)
}

pub fn into_polling(self) -> Result<PreallocatedPolling<'o>, Error>

Call this method to enable asynchronous polling mode on the statement

Trait Implementations

impl<'o> AsStatementRef for Preallocated<'o>

fn as_stmt_ref(&mut self) -> StatementRef<'_>

Get an exclusive reference to the underlying statement handle. This method is used to implement other more higher level methods on top of it. It is not intended to be called by users of this crate directly, yet it may serve as an escape hatch for low level use cases.