Transformation modules C API

This is the additional API documentation for mg_procedure.h that contains declarations of all functions that can be used to implement a transformation. The source file can be found in the Memgraph installation directory, under include/memgraph. On the standard Debian installation, this will be under /usr/include/memgraph.

caution

NOTE: This part of the documentation is still under development. An updated version will soon be available.

Types

	Name
typedef void (*)(const struct mgp_messages *, const struct mgp_graph *, struct mgp_result *, struct mgp_memory *);	mgp_trans_cb Entry-point for a transformation with a fixed result type

Each record of the result must contain the following fields:

• the query field with a Cypher query as a string that will be executed against the database
• the parameters field with the optional query parameters as a nullable map

Functions

	Name
size_t	mgp_messages_size(const struct mgp_messages *messages) Get the number of messages contained in the messages list.
const struct mgp_message *	mgp_messages_at(const struct mgp_messages *messages, size_t idx) Get the mgp_message at index idx.
size_t	mgp_message_payload_size(const struct mgp_message *message) Get the payload size of message.
const char *	mgp_message_payload(const struct mgp_message *message) Get the payload of messages as a byte array.
const char *	mgp_message_topic_name(const struct mgp_message *message) Get the topic name of message.
size_t	mgp_message_key_size(const struct mgp_message *message) Get key size of message.
const char *	mgp_message_key(const struct mgp_message *message) Get key of message as a byte array.
int64_t	mgp_message(const struct mgp_message *message) Get the timestamp of message.
int	mgp_module_add_transformation(struct mgp_module *module, const char *name, mgp_trans_cb cb) Registers a transformation to a module

Types Documentation

typedef mgp_trans_cb

typedef void(* mgp_trans_cb) (const struct mgp_messages *, const struct mgp_graph *, struct mgp_result *, struct mgp_memory *);

Entry-point for a transformation invoked through a stream. Passed in arguments will not live longer than the callback's execution. Therefore, you must not store them globally or use the passed in mgp_memory to allocate global resources. The result type of transformation is fixed.

Functions Documentation

function mgp_messages_size

size_t mgp_messages_size(
  const struct mgp_messages* messages
)

Returns the total number of messages contained in the argument messages.

function mgp_messages_at

mgp_message* mgp_messages_at(
  const struct mgp_messages* messages,
  size_t idx
)

Accessor function that returns the underlying message stored at index idx in messages. The index supplied must reside in the half-open interval [0, mgp_messages_size(messages)).

function mgp_message_payload_size

size_t mgp_message_payload_size
  const struct mgp_message* message
)

Returns the payload size of the argument message.

function mgp_message_payload

const char * mgp_message_payload(
  const struct mgp_message* message
)

Returns the payload of the argument message as a byte array with size mgp_message_payload_size(message).

function mgp_message_topic_name

const char * mgp_message_topic_name(
  const struct mgp_message* message
)

Returns topic name of the argument message. Topic name is NULL terminated.

function mgp_message_key_size

size_t mgp_message_key_size(
  const struct mgp_message* message
)

Returns the key size of argument message.

function mgp_message_key

const char * mgp_message_key(
  const struct mgp_message* message
)

Returns the key of the argument message as a byte array with size mgp_message_key_size(message).

function mgp_message_timestamp

int64_t mgp_timestamp(
  const struct mgp_message* message
)

Returns the timestamp of the argument message.

function mgp_module_add_transformation

int mgp_module_add_transformation(
  struct mgp_module *module,
  const char *name,
  mgp_trans_cb cb
)

Register a transformation to a module. The name must be a sequence of digits, underscores, lowercase, and uppercase Latin letters. The name must begin with a non-digit character. Note that Unicode characters are not allowed. Additionally, the name is case-sensitive.

Return non-zero if the transformation is added successfully. Registering might fail if unable to allocate memory for the transformation; if name is not valid, or a transformation with the same name was already registered or if any other unexpected failure happens.