Trait MergeOperator

pub trait MergeOperator<K, V>: Fn(K, Option<V>, V) -> Option<V>
where
    K: Key,
    V: Value,
{ }

Examples

use sled::{Config, IVec};

fn concatenate_merge(
  _key: String,               // the key being merged
  old_value: Option<Vec<f32>>,  // the previous value, if one existed
  merged_bytes: Vec<f32>        // the new bytes being merged in
) -> Option<Vec<f32>> {       // set the new value, return None to delete
  let mut ret = old_value
    .map(|ov| ov.to_vec())
    .unwrap_or_else(|| vec![]);

  ret.extend_from_slice(&merged_bytes);

  Some(ret)
}

let db = sled::Config::new()
  .temporary(true).open()?;

let tree = bincode_sled::Tree::<String, Vec<f32>>::open(&db, "unique_id");
tree.set_merge_operator(concatenate_merge);

let k = String::from("some_key");

tree.insert(&k, &vec![0.0]);
tree.merge(&k, &vec![1.0]);
tree.merge(&k, &vec![2.0]);
assert_eq!(tree.get(&k)?, Some(vec![0.0, 1.0, 2.0]));

// Replace previously merged data. The merge function will not be called.
tree.insert(&k, &vec![3.0]);
assert_eq!(tree.get(&k)?, Some(vec![3.0]));

// Merges on non-present values will cause the merge function to be called
// with `old_value == None`. If the merge function returns something (which it
// does, in this case) a new value will be inserted.
tree.remove(&k);
tree.merge(&k, &vec![4.0]);
assert_eq!(tree.get(&k)?, Some(vec![4.0]));

Implementors

impl<K: Key, V: Value, F> MergeOperator<K, V> for F

where F: Fn(K, Option<V>, V) -> Option<V>,