Enum Form 

#[non_exhaustive]
pub enum Form<'a> {
    RowLock,
    Lease(Column<'a>),
    Advisory(&'a [KeyPart<'a>]),
}

How a subscription claims the rows of a table; a table has exactly one form.

The lease form carries its locked_until column and the advisory form its key, so a table cannot declare two forms. The row lock is the default: the form of a table that declares neither.

Examples

A settlement of a dialect of the service’s own follows the form:

use ruststream_sqlx_dialect::{Dialect, Form, Param, Statement, StatementError, TableSpec};

/// SQL Server, a database without a built-in dialect.
#[derive(Debug)]
pub struct Mssql;

impl Dialect for Mssql {
    fn name(&self) -> &'static str {
        "mssql"
    }

    fn ack(&self, spec: &TableSpec<'_>) -> Result<Statement, StatementError> {
        let mut sql = String::from("DELETE FROM ");
        self.quote_into(spec.table(), &mut sql);
        sql.push_str(" WHERE ");
        self.quote_into(spec.id().name(), &mut sql);
        sql.push_str(" = @p1");
        match spec.form() {
            // In the lease form the row goes only while it holds the delivery's lease.
            Form::Lease(expiry) => {
                sql.push_str(" AND ");
                self.quote_into(expiry.name(), &mut sql);
                sql.push_str(" = @p2");
                Ok(Statement::new(sql, [Param::Id, Param::Held]))
            }
            _ => Ok(Statement::new(sql, [Param::Id])),
        }
    }
}

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

RowLock

Rows stay locked in a transaction held for the whole handler; the default.

Lease(Column<'a>)

A claim sets this column, the lease’s expiry, and commits; the value holds the row.

Advisory(&'a [KeyPart<'a>])

A session lock on the key these parts build from the row holds the row.

Implementations

impl Form<'_>

pub const fn name(&self) -> &'static str

The form’s name in messages: row lock, lease or advisory lock.

Examples

use ruststream_sqlx_dialect::{Dialect, Form, Param, Statement, StatementError, TableSpec};

/// SQL Server, a database without a built-in dialect.
#[derive(Debug)]
pub struct Mssql;

impl Dialect for Mssql {
    fn name(&self) -> &'static str {
        "mssql"
    }

    fn ack(&self, spec: &TableSpec<'_>) -> Result<Statement, StatementError> {
        // This dialect serves the row lock form alone, and its refusal names the table's
        // form.
        if spec.form() != Form::RowLock {
            return Err(StatementError::UnsupportedForm {
                dialect: self.name(),
                form: spec.form().name(),
            });
        }
        let mut sql = String::from("DELETE FROM ");
        self.quote_into(spec.table(), &mut sql);
        sql.push_str(" WHERE ");
        self.quote_into(spec.id().name(), &mut sql);
        sql.push_str(" = @p1");
        Ok(Statement::new(sql, [Param::Id]))
    }
}

Trait Implementations

impl<'a> Clone for Form<'a>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<'a> Copy for Form<'a>

impl<'a> Debug for Form<'a>

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

Formats the value using the given formatter.

impl<'a> Default for Form<'a>

fn default() -> Self

Returns the “default value” for a type.

impl<'a> Eq for Form<'a>

impl<'a> Hash for Form<'a>

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<'a> PartialEq for Form<'a>

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl<'a> StructuralPartialEq for Form<'a>