Joined Store

class encore.storage.joined_store.JoinedStore(stores)

A key-value store that joins together several other Key-Value Stores

A joined store is a composite store which takes a list of stores and presents a set of keys that is the union of all the keys that are available in all the stores. When a key is available in multiple stores, then the store which comes first in the list has priority.

All writes are performed into the first store in the list.

Parameters:

• event_manager – An event_manager which implements the BaseEventManager API.

• stores (list of stores) – The stores that are joined together by this store.

__init__(stores)

connect(credentials=None)

Connect to the key-value store, optionally with authentication

This method creates or connects to any long-lived resources that the store requires.

Parameters:

credentials – An object that can supply appropriate credentials to to authenticate the use of any required resources. The exact form of the credentials is implementation-specific, but may be as simple as a (username, password) tuple.

delete(key)

Delete a key from the repsository.

This may be left unimplemented by subclasses that represent a read-only key-value store.

Parameters:

• key (string) – The key for the resource in the key-value store. They key is a unique identifier for the resource within the key-value store.

• Events –

• ------ –

• StoreDeleteEvent – On successful completion of a transaction, a StoreDeleteEvent should be emitted with the key.

disconnect()

Disconnect from the key-value store

This method disposes or disconnects to any long-lived resources that the store requires.

exists(key)

Test whether or not a key exists in the key-value store

Parameters:

key (string) – The key for the resource in the key-value store. They key is a unique identifier for the resource within the key-value store.

Returns:

exists – Whether or not the key exists in the key-value store.

Return type:

bool

from_bytes(key, data, buffer_size=1048576)

Efficiently store a bytes object as the data associated with a key.

This method can be optionally overriden by subclasses to proved a more efficient way of copy the data from a bytes object to the underlying data store. The default implementation uses the set() method together with a cStringIO.

Parameters:

• key (string) – The key for the resource in the key-value store. They key is a unique identifier for the resource within the key-value store.

• data (bytes) – The data as a bytes object.

• buffer_size (int) – An optional indicator of the number of bytes to read at a time. Implementations are free to ignore this hint or use a different default if they need to. The default is 1048576 bytes (1 MiB).

from_file(key, path, buffer_size=1048576)

Efficiently read data from a file into a key in the key-value store.

This method can be optionally overriden by subclasses to proved a more efficient way of copy the data from a path in the filesystem to the underlying data store. The default implementation uses the set() method together with chunked reads from the disk which are fed into the data stream.

This makes no attempt to set metadata.

Parameters:

• key (string) – The key for the resource in the key-value store. They key is a unique identifier for the resource within the key-value store.

• path (string) – A file system path to read the data from.

• buffer_size (int) – An optional indicator of the number of bytes to read at a time. Implementations are free to ignore this hint or use a different default if they need to. The default is 1048576 bytes (1 MiB).

get(key)

Retrieve a stream of data and metdata from a given key in the key-value store.

Parameters:

key (string) – The key for the resource in the key-value store. They key is a unique identifier for the resource within the key-value store.

Returns:

• data (file-like) – A readable file-like object that provides stream of data from the key-value store

• metadata (dictionary) – A dictionary of metadata for the key.

Raises:

KeyError : – If the key is not found in the store, a KeyError is raised.

get_data(key)

Retrieve a stream from a given key in the key-value store.

Parameters:

key (string) – The key for the resource in the key-value store. They key is a unique identifier for the resource within the key-value store.

Returns:

data – A readable file-like object the that provides stream of data from the key-value store.

Return type:

file-like

Raises:

KeyError : – This will raise a key error if the key is not present in the store.

get_metadata(key, select=None)

Retrieve the metadata for a given key in the key-value store.

Parameters:

• key (string) – The key for the resource in the key-value store. They key is a unique identifier for the resource within the key-value store.

• select (iterable of strings or None) – Which metadata keys to populate in the result. If unspecified, then return the entire metadata dictionary.

Returns:

metadata – A dictionary of metadata associated with the key. The dictionary has keys as specified by the select argument. If a key specified in select is not present in the metadata, then it will not be present in the returned value.

Return type:

dict

Raises:

KeyError : – This will raise a key error if the key is not present in the store.

glob(pattern)

Return keys which match glob-style patterns

Parameters:

pattern (string) – Glob-style pattern to match keys with.

Returns:

result – A iterable of keys which match the glob pattern.

Return type:

iterable

is_connected()

Whether or not the store is currently connected

Returns:

connected – Whether or not the store is currently connected.

Return type:

bool

multiget(keys)

Retrieve the data and metadata for a collection of keys.

Parameters:

keys (iterable of strings) – The keys for the resources in the key-value store. Each key is a unique identifier for a resource within the key-value store.

Returns:

result – An iterator of (data, metadata) pairs.

Return type:

iterator of (file-like, dict) tuples

Raises:

KeyError : – This will raise a key error if the key is not present in the store.

multiget_data(keys)

Retrieve the data for a collection of keys.

Parameters:

keys (iterable of strings) – The keys for the resources in the key-value store. Each key is a unique identifier for a resource within the key-value store.

Returns:

result – An iterator of file-like data objects corresponding to the keys.

Return type:

iterator of file-like

Raises:

KeyError : – This will raise a key error if the key is not present in the store.

multiget_metadata(keys, select=None)

Retrieve the metadata for a collection of keys in the key-value store.

Parameters:

• keys (iterable of strings) – The keys for the resources in the key-value store. Each key is a unique identifier for a resource within the key-value store.

• select (iterable of strings or None) – Which metadata keys to populate in the results. If unspecified, then return the entire metadata dictionary.

Returns:

metadatas – An iterator of dictionaries of metadata associated with the key. The dictionaries have keys as specified by the select argument. If a key specified in select is not present in the metadata, then it will not be present in the returned value.

Return type:

iterator of dicts

Raises:

KeyError : – This will raise a key error if the key is not present in the store.

multiset(keys, values, buffer_size=1048576)

Set the data and metadata for a collection of keys.

Where supported by an implementation, this should perform the whole collection of sets as a single transaction.

Like zip() if keys and values have different lengths, then any excess values in the longer list should be silently ignored.

Parameters:

• keys (iterable of strings) – The keys for the resources in the key-value store. Each key is a unique identifier for a resource within the key-value store.

• values (iterable of (file-like, dict) tuples) – An iterator that provides the (data, metadata) pairs for the corresponding keys.

• buffer_size (int) – An optional indicator of the number of bytes to read at a time. Implementations are free to ignore this hint or use a different default if they need to. The default is 1048576 bytes (1 MiB).

• Events –

• ------ –

• StoreProgressStartEvent – For buffering implementations, this event should be emitted prior to writing any data to the underlying store.

• StoreProgressStepEvent – For buffering implementations, this event should be emitted periodically as data is written to the underlying store.

• StoreProgressEndEvent – For buffering implementations, this event should be emitted after finishing writing to the underlying store.

• StoreSetEvent – On successful completion of a transaction, a StoreSetEvent should be emitted with the key & metadata for each key that was set.

multiset_data(keys, datas, buffer_size=1048576)

Set the data for a collection of keys.

Where supported by an implementation, this should perform the whole collection of sets as a single transaction.

Like zip() if keys and datas have different lengths, then any excess values in the longer list should be silently ignored.

Parameters:

• keys (iterable of strings) – The keys for the resources in the key-value store. Each key is a unique identifier for a resource within the key-value store.

• datas (iterable of file-like objects) – An iterator that provides the data file-like objects for the corresponding keys.

• buffer_size (int) – An optional indicator of the number of bytes to read at a time. Implementations are free to ignore this hint or use a different default if they need to. The default is 1048576 bytes (1 MiB).

• Events –

• ------ –

• StoreProgressStartEvent – For buffering implementations, this event should be emitted prior to writing any data to the underlying store.

• StoreProgressStepEvent – For buffering implementations, this event should be emitted periodically as data is written to the underlying store.

• StoreProgressEndEvent – For buffering implementations, this event should be emitted after finishing writing to the underlying store.

• StoreSetEvent – On successful completion of a transaction, a StoreSetEvent should be emitted with the key & metadata for each key that was set.

multiset_metadata(keys, metadatas)

Set the metadata for a collection of keys.

Where supported by an implementation, this should perform the whole collection of sets as a single transaction.

Like zip() if keys and metadatas have different lengths, then any excess values in the longer list should be silently ignored.

Parameters:

• keys (iterable of strings) – The keys for the resources in the key-value store. Each key is a unique identifier for a resource within the key-value store.

• metadatas (iterable of dicts) – An iterator that provides the metadata dictionaries for the corresponding keys.

• Events –

• ------ –

• StoreSetEvent – On successful completion of a transaction, a StoreSetEvent should be emitted with the key & metadata for each key that was set.

multiupdate_metadata(keys, metadatas)

Update the metadata for a collection of keys.

Where supported by an implementation, this should perform the whole collection of sets as a single transaction.

Like zip() if keys and metadatas have different lengths, then any excess values in the longer list should be silently ignored.

Parameters:

• keys (iterable of strings) – The keys for the resources in the key-value store. Each key is a unique identifier for a resource within the key-value store.

• metadatas (iterable of dicts) – An iterator that provides the metadata dictionaries for the corresponding keys.

• Events –

• ------ –

• StoreSetEvent – On successful completion of a transaction, a StoreSetEvent should be emitted with the key & metadata for each key that was set.

query(select=None, **kwargs)

Query for keys and metadata matching metadata provided as keyword arguments

This provides a very simple querying interface that returns precise matches with the metadata. If no arguments are supplied, the query will return the complete set of metadata for the key-value store.

Parameters:

• select (iterable of strings or None) – An optional list of metadata keys to return. If this is not None, then the metadata dictionaries will only have values for the specified keys populated.

• kwargs – Arguments where the keywords are metadata keys, and values are possible values for that metadata item.

Returns:

result – An iterable of (key, metadata) tuples where metadata matches all the specified values for the specified metadata keywords. If a key specified in select is not present in the metadata of a particular key, then it will not be present in the returned value.

Return type:

iterable

query_keys(**kwargs)

Query for keys matching metadata provided as keyword arguments

This provides a very simple querying interface that returns precise matches with the metadata. If no arguments are supplied, the query will return the complete set of keys for the key-value store.

This is equivalent to self.query(**kwargs).keys(), but potentially more efficiently implemented.

Parameters:

kwargs – Arguments where the keywords are metadata keys, and values are possible values for that metadata item.

Returns:

result – An iterable of key-value store keys whose metadata matches all the specified values for the specified metadata keywords.

Return type:

iterable

set(key, value, buffer_size=1048576)

Store a stream of data into a given key in the key-value store.

This may be left unimplemented by subclasses that represent a read-only key-value store.

Parameters:

• key (string) – The key for the resource in the key-value store. They key is a unique identifier for the resource within the key-value store.

• value (tuple of file-like, dict) – A pair of objects, the first being a readable file-like object that provides stream of data from the key-value store. The second is a dictionary of metadata for the key.

• buffer_size (int) – An optional indicator of the number of bytes to read at a time. Implementations are free to ignore this hint or use a different default if they need to. The default is 1048576 bytes (1 MiB).

• Events –

• ------ –

• StoreProgressStartEvent – For buffering implementations, this event should be emitted prior to writing any data to the underlying store.

• StoreProgressStepEvent – For buffering implementations, this event should be emitted periodically as data is written to the underlying store.

• StoreProgressEndEvent – For buffering implementations, this event should be emitted after finishing writing to the underlying store.

• StoreSetEvent – On successful completion of a transaction, a StoreSetEvent should be emitted with the key & metadata

set_data(key, data, buffer_size=1048576)

Replace the data for a given key in the key-value store.

Parameters:

• key (string) – The key for the resource in the key-value store. They key is a unique identifier for the resource within the key-value store.

• data (file-like) – A readable file-like object the that provides stream of data from the key-value store.

• buffer_size (int) – An optional indicator of the number of bytes to read at a time. Implementations are free to ignore this hint or use a different default if they need to. The default is 1048576 bytes (1 MiB).

• Events –

• ------ –

• StoreProgressStartEvent – For buffering implementations, this event should be emitted prior to writing any data to the underlying store.

• StoreProgressStepEvent – For buffering implementations, this event should be emitted periodically as data is written to the underlying store.

• StoreProgressEndEvent – For buffering implementations, this event should be emitted after finishing writing to the underlying store.

• StoreSetEvent – On successful completion of a transaction, a StoreSetEvent should be emitted with the key & metadata

set_metadata(key, metadata)

Set new metadata for a given key in the key-value store.

This replaces the existing metadata set for the key with a new set of metadata.

Parameters:

• key (string) – The key for the resource in the key-value store. They key is a unique identifier for the resource within the key-value store.

• metadata (dict) – A dictionary of metadata to associate with the key. The dictionary keys should be strings which are valid Python identifiers.

• Events –

• ------ –

• StoreSetEvent – On successful completion of a transaction, a StoreSetEvent should be emitted with the key & metadata

to_bytes(key, buffer_size=1048576)

Efficiently store the data associated with a key into a bytes object.

This method can be optionally overriden by subclasses to proved a more efficient way of copy the data from the underlying data store to a bytes object. The default implementation uses the get() method together with chunked reads from the returned data stream and join.

Parameters:

• key (string) – The key for the resource in the key-value store. They key is a unique identifier for the resource within the key-value store.

• buffer_size (int) – An optional indicator of the number of bytes to read at a time. Implementations are free to ignore this hint or use a different default if they need to. The default is 1048576 bytes (1 MiB).

Returns:

• bytes – The contents of the file-like object as bytes.

• Events

• ——

• StoreProgressStartEvent – For buffering implementations, this event should be emitted prior to extracting the data.

• StoreProgressStepEvent – For buffering implementations, this event should be emitted periodically as data is extracted.

• StoreProgressEndEvent – For buffering implementations, this event should be emitted after extracting the data.

to_file(key, path, buffer_size=1048576)

Efficiently store the data associated with a key into a file.

This method can be optionally overriden by subclasses to proved a more efficient way of copy the data from the underlying data store to a path in the filesystem. The default implementation uses the get() method together with chunked reads from the returned data stream to the disk.

Parameters:

• key (string) – The key for the resource in the key-value store. They key is a unique identifier for the resource within the key-value store.

• path (string) – A file system path to store the data to.

• buffer_size (int) – An optional indicator of the number of bytes to read at a time. Implementations are free to ignore this hint or use a different default if they need to. The default is 1048576 bytes (1 MiB).

• Events –

• ------ –

• StoreProgressStartEvent – For buffering implementations, this event should be emitted prior to writing any data to disk.

• StoreProgressStepEvent – For buffering implementations, this event should be emitted periodically as data is written to disk.

• StoreProgressEndEvent – For buffering implementations, this event should be emitted after finishing writing to disk.

transaction(notes)

Provide a transaction context manager

Implementations which have no native notion of transactions may choose not to implement this.

This method provides a context manager which creates a data store transaction in its __enter__() method, and commits it in its __exit__() method if no errors occur. Intended usage is:

with repo.transaction("Writing data..."):
    # everything written in this block is part of the transaction
    ...

If the block exits without error, the transaction commits, otherwise the transaction should roll back the state of the underlying data store to the start of the transaction.

Parameters:

notes (string) – Some information about the transaction, which may or may not be used by the implementation.

Returns:

• transaction (context manager) – A context manager for the transaction.

• Events

• ——

• StoreTransactionStartEvent – This event should be emitted on entry into the transaction.

• StoreProgressStartEvent – For buffering implementations, this event should be emitted prior to writing any data to the underlying store.

• StoreProgressStepEvent – For buffering implementations, this event should be emitted periodically as data is written to the underlying store.

• StoreProgressEndEvent – For buffering implementations, this event should be emitted after finishing writing to the underlying store.

• StoreTransactionEndEvent – This event should be emitted on successful conclusion of the transaction, before any Set or Delete events are emitted.

• StoreSetEvent – On successful completion of a transaction, a StoreSetEvent should be emitted with the key & metadata for each key that was set during the transaction.

• StoreDeleteEvent – On successful completion of a transaction, a StoreDeleteEvent should be emitted with the key for all deleted keys.

update_metadata(key, metadata)

Update the metadata for a given key in the key-value store.

This performs a dictionary update on the existing metadata with the provided metadata keys and values

Parameters:

• key (string) – The key for the resource in the key-value store. They key is a unique identifier for the resource within the key-value store.

• metadata (dict) – A dictionary of metadata to associate with the key. The dictionary keys should be strings which are valid Python identifiers.

• Events –

• ------ –

• StoreSetEvent – On successful completion of a transaction, a StoreSetEvent should be emitted with the key & metadata