Moneta Specification

(See RFC 2119 for use of MUST, SHOULD, MAY, MUST NOT, and SHOULD NOT)

The purpose of the moneta specification is to create a general-purpose API for interacting with key-value stores. In general, libraries that need to interact with key-value stores should be able to specify that they can use any "moneta-compliant store". Moneta ships with a set of executable specs which you can use to verify spec-compliance with your moneta adapter.

Class Methods

new(options[Hash] => {}) => Object

Return an instance of the moneta adapter, with the instance methods listed below. The options hash is a required parameter, and the adapter may specify whatever additional requirements it needs to properly instantiate it.

Instance Methods

[](key[Object]) => Object

Return the value stored in the key-value-store under the provided key. Adapters MUST return a duplicate of the original value, and consumers should expect that adapters might serialize and deserialize the key and value. As a result, both the key and value MUST be objects that can be serialized using Ruby's Marshal system.

[]=(key[Object], value[Object]) => Object(value)

Store the value in the key-value-store under the provided key. Adapters MAY serialize the value using Ruby's Marshal system, and MUST NOT store a reference to the original value in the store, unless Ruby disallows duplication of the original value. Adapters SHOULD NOT simply call dup on the value, unless the value stores no references to other Object. For example, an adapter MAY store a dup of a String, but SHOULD NOT store a dup of ["hello", "world"].

fetch(key[Object], options[Hash] => {}, &block) => Object

Return the value stored in the key-value-store under the provided key. If no value is stored under the provided key, the adapter MUST yield to the block, and return the value. The adapter MUST NOT store the value returned from the block in the key-value-store.

fetch(key[Object], value[Object], options[Hash] => {}) => Object

Return the value stored in the key-value-store under the provided key. If no value is stored under the provided key, the adapter MUST return the default value provided. The adapter MUST NOT store the default value in the key-value-store.

delete(key[Object], options[Hash] => {}) => Object

Delete the value stored in the key-value-store for the key provided, and return the value previously stored there. After this operation, the key-value-store MUST behave as though no value was stored for the provided key.

key?(key[Object], options[Hash] => {}) => [TrueClass, FalseClass]

Determine whether a value exists in the key-value-store for the key provided. If a value exists, the adapter MUST return true. Otherwise, the adapter MUST return false.

store(key[Object], value[Object], options[Hash] => {}) => Object(value)

Behaves the same as []=, but allows the client to send additional options which can be specified by the adapter (and which may be specified by extensions to this specification).

increment(key[Object], amount[Integer] = 1, options[Hash] => {}) => Integer(value)

Increments a value atomically. This method is not supported by all stores and might raise a NotImplementedError. This method MUST accept negative amounts, but the result MUST be unsigned.

decrement(key[Object], amount[Integer] = 1, options[Hash] => {}) => Integer(value)

Decrements a value atomically. This method is not supported by all stores and might raise a NotImplementedError. This method MUST accept negative amounts, but the result MUST be unsigned.

create(key[Object], value[Object], options[Hash] => {}) => [TrueClass, FalseClass]

Creates a value atomically. This method is not supported by all stores and might raise a NotImplementedError. It MUST return true if the value was created.

clear(options[Hash] => {})

Completely empty all keys and values from the key-value-store. Adapters MAY allow a namespace during initialization, which can scope this operation to a particular subset of keys. After calling clear, a [] operation MUST return nil for every possible key, and a key? query MUST return false for every possible key.

close

Closes the store

features => Array<Symbol> and supports?(Symbol) => [TrueClass, FalseClass]

Feature detection. Adapters MUST return :create and :increment if these methods are supported.

each_key => Enumerator and each_key(&block) => Object

Enumerates over the keys in the store. This method is not supported by all stores. When not supported, this method MUST raise a NotImplementedError, regardless of whether a block is supplied. When supported, this method allows traversal of all keys in the store. The method behaves differently depending on whether a block is supplied. In either case, for each key, k in the traversal, key?(k) MUST return true; and for each key, k for which key?(k) returns true, k MUST be traversed by each_key. Keys MAY be traversed in any order. Mutation of the store while traversing keys MAY be allowed. Querying the store (calling fetch, key?, etc.) while traversing MUST be allowed.

  • If no block is supplied, each_key MUST return an Enumerator that can be used to traverse each key (e.g. by calling each). Calling methods on the Enumerator such as each with a block MUST return the store object.

  • If a block is supplied, that block MUST be called once with each traversed key as the only argument. When called in this way, each_key MUST return the store object.

values_at(*keys[Array<Object>], **options[Hash]) => Array

Returns an array containing the values associated with the given keys, in the same order as the supplied keys. If a key is not present in the key-value-store, nil MUST be returned in its place. For each key, and each value, the same restrictions apply as apply to individual keys passed to, and values received from the store in the specification of [] (see above). The adapter MAY perform this operation atomically.

fetch_values(*keys[Array<Object>], **options[Hash], &defaults) => Array

Behaves identically to values_at, except that it MUST accept an optional block. When supplied, the block will be called successively with each supplied key that is not present in the store. The return value of the block call MUST be used in place of nil in returned the array of values. As with fetch (above), the adapter MUST NOT store the return value of the block call in the key-value-store. The adapter MAY perform this operation atomically.

slice(*keys[Array<Object>], **options[Hash]) => <Array(Object, Object)>

Returns a collection of key-value pairs corresponding to those supplied keys which are present in the key-value store, and their associated values. A key MUST be present in the return value if and only if it was supplied in the keys parameter and it is present in the key-value store. For each key, and each value, the same restrictions apply as apply to individual keys passed to, and values received from the store in the specification of [] (see above). The adapter MAY perform this operation atomically.

merge!(pairs[<Array(Object, Object)>], options[Hash] => {}, &block) => Object

Stores the pairs in the key-value-store, and returns the store object. This method MUST behave identically to successively calling []= with each key-value pair and the options hash; except that the adapter MAY perform this operation atomically, and the method MUST accept an optional block, which MUST be called for each key that is to be overwritten. When the block is provided, it MUST be called before overwriting any existing values with the key, old value and supplied value, and the return value of the block MUST be used in place of the supplied value.

Additional Options Hashes

The following methods may all take an additional Hash as a final argument. This allows the client to send additional options which can be specified by the adapter (and which may be specified by extensions to this specification). The methods MUST NOT modify the supplied option hash.

  • fetch
  • load
  • store
  • delete
  • key?
  • increment
  • clear
  • merge!

Additionally, the following methods accept options as keyword arguments, after non-keyword arguments. These keyword arguments are treated as a hash, equivalent to supplying a hash to the above methods.

  • values_at
  • fetch_values
  • slice

In the case of methods with optional arguments, the Hash MUST be provided as the final argument. Keys in this Hash MUST be Symbols.

Atomicity

The base Moneta specification does not specify any atomicity guarantees. However, extensions to this spec may specify extensions that define additional guarantees for any of the defined operations.