Struct mz_stash::TableTransaction

pub struct TableTransaction<K, V> {
    pub(crate) initial: BTreeMap<K, V>,
    pub(crate) pending: BTreeMap<K, Option<V>>,
    pub(crate) uniqueness_violation: fn(a: &V, b: &V) -> bool,
}

TableTransaction emulates some features of a typical SQL transaction over table for a StashCollection.

It supports:

• uniqueness constraints
• transactional reads and writes (including read-your-writes before commit)

K is the primary key type. Multiple entries with the same key are disallowed. V is the an arbitrary value type.

To finalize, add the results of TableTransaction::pending() to an AppendBatch.

Fields

initial: BTreeMap<K, V>

pending: BTreeMap<K, Option<V>>

uniqueness_violation: fn(a: &V, b: &V) -> bool

Implementations

impl<K, V> TableTransaction<K, V> where
    K: Ord + Eq + Hash + Clone,
    V: Ord + Clone, 

pub fn new(
    initial: BTreeMap<K, V>,
    uniqueness_violation: fn(a: &V, b: &V) -> bool
) -> Self

Create a new TableTransaction with initial data. uniqueness_violation is a function whether there is a uniqueness violation among two values.

pub fn pending(self) -> Vec<(K, V, Diff)>

Consumes and returns the pending changes and their diffs. Diff is guaranteed to be 1 or -1.

pub(crate) fn verify(&self) -> Result<(), StashError>

pub fn for_values<F: FnMut(&K, &V)>(&self, f: F)

Iterates over the items viewable in the current transaction in arbitrary order.

pub fn items(&self) -> BTreeMap<K, V>

Returns the items viewable in the current transaction.

pub(crate) fn for_values_mut<F: FnMut(&mut BTreeMap<K, Option<V>>, &K, &V)>(
    &mut self,
    f: F
)

Iterates over the items viewable in the current transaction, and provides a Vec where additional pending items can be inserted, which will be appended to current pending items. Does not verify unqiueness.

pub fn insert(&mut self, k: K, v: V) -> Result<(), ()>

Inserts a new k,v pair.

Returns an error if the uniqueness check failed or the key already exists.

pub fn update<F: Fn(&K, &V) -> Option<V>>(
    &mut self,
    f: F
) -> Result<Diff, StashError>

Updates k, v pairs. f is a function that can return Some(V) if the value should be updated, otherwise None. Returns the number of changed entries.

Returns an error if the uniqueness check failed.

pub fn delete<F: Fn(&K, &V) -> bool>(&mut self, f: F) -> Vec<(K, V)>

Deletes items for which f returns true. Returns the keys and values of the deleted entries.