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 + Clone, V: Ord + Clone,

pub fn new<KP, VP>( initial: BTreeMap<KP, VP>, uniqueness_violation: fn(a: &V, b: &V) -> bool ) -> Result<Self, TryFromProtoError>where K: RustType<KP>, V: RustType<VP>,

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

Internally the Stash serializes data as protobuf. All fields in a proto message are optional, which makes using them in Rust cumbersome. Generic parameters KP and VP are protobuf types which deserialize to K and V that a TableTransaction is generic over.

pub fn pending<KP, VP>(self) -> Vec<(KP, VP, Diff)>where K: RustType<KP>, V: RustType<VP>,

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 get(&self, k: &K) -> Option<&V>

Returns the current value of k.

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<(), StashError>

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

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

Returns an error if the uniqueness check failed.

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

Set the value for a key. Returns the previous entry if the key existed, otherwise None.

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.