Query modules C++ API

This is the API documentation for mgp.hpp, which contains declarations of all functions in the C++ API for implementing query module procedures and functions. The source file can be found in the Memgraph installation directory, under /usr/include/memgraph.

To see how to implement query modules in C++, take a look at the example we provided.

If you install any C++ modules after running Memgraph, you’ll need to load them into Memgraph or restart Memgraph in order to use them.

Functions and procedures

With this API it’s possible to extend your Cypher queries with functions and procedures with AddProcedure and AddFunction.

The API needs memory access to add procedures and functions, this can be done with either mgp::MemoryDispatcherGuard guard(memory); or mgp::memory = memory;, where the use of the former is advised since mgp::memory = memory; is not thread-safe and will be deprecated in the future.

Functions are simple operations that return a single value and can be used in any expression or predicate.

Procedures are more complex computations that may modify the graph, and their output is available to later processing steps in your query. A procedure may only be run from CALL clauses. The output is a stream of records that is made accessible with a YIELD clause.

AddProcedure

Add a procedure to your query module. The procedure is registered as [QUERY_MODULE_NAME].[PROC_NAME] and can be used in Cypher queries.

void AddProcedure(
    mgp_proc_cb callback,
    std::string_view name,
    ProcedureType proc_type,
    std::vector<Parameter> parameters,
    std::vector<Return> returns,
    mgp_module *module,
    mgp_memory *memory);

{

Input:

• callback: procedure callback
• name: procedure name
• proc_type: procedure type (read/write)
• parameters: vector (list) of procedure parameters
• returns: vector (list) of procedure return values
• module: the query module that the procedure is added to
• memory: access to memory

ProcedureType

Enum class for Cypher procedure types.

• ProcedureType::Read: read procedure
• ProcedureType::Write: write procedure

AddBatchProcedure

Add a batch procedure to your query module. The procedure is registered as [QUERY_MODULE_NAME].[PROC_NAME] and can be used in Cypher queries.

void AddBatchProcedure(
    mgp_proc_cb callback,
    mgp_proc_initializer initializer,
    mgp_proc_cleanup cleanup,
    std::string_view name,
    ProcedureType proc_type,
    std::vector<Parameter> parameters,
    std::vector<Return> returns,
    mgp_module *module,
    mgp_memory *memory);

{

Input:

• callback: procedure callback, invoked through OpenCypher
• initializer: procedure initializer, invoked before callback
• cleanup: procedure cleanup, invoked after batching is done
• name: procedure name
• proc_type: procedure type (read/write)
• parameters: vector (list) of procedure parameters
• returns: vector (list) of procedure return values
• module: the query module that the procedure is added to
• memory: access to memory

ProcedureType

Enum class for Cypher procedure types.

• ProcedureType::Read: read procedure
• ProcedureType::Write: write procedure

AddFunction

Add a function to your query module. The function is registered as [QUERY_MODULE_NAME].[FUNC_NAME] and can be used in Cypher queries.

void AddFunction(
    mgp_func_cb callback,
    std::string_view name,
    std::vector<Parameter> parameters,
    std::vector<Return> returns,
    mgp_module *module,
    mgp_memory *memory);

{

Input:

• callback: function callback
• name: function name
• parameters: vector (list) of function parameters
• returns: vector (list) of function return values
• module: the query module that the procedure is added to
• memory: access to memory

Parameter

Represents a procedure/function parameter. Parameters are defined by their name, type, and (if optional) default value.

Constructors

Creates a non-optional parameter with the given name and type.

Parameter(std::string_view name, Type type)

Creates an optional Boolean parameter with the given name and default_value.

Parameter(std::string_view name, Type type, bool default_value)

Creates an optional integer parameter with the given name and default_value.

Parameter(std::string_view name, Type type, int default_value)

Creates an optional floating-point parameter with the given name and default_value.

Parameter(std::string_view name, Type type, double default_value)

Creates an optional string parameter with the given name and default_value.

Parameter(std::string_view name, Type type, std::string_view default_value)
Parameter(std::string_view name, Type type, const char *default_value)

Creates a non-optional list parameter with the given name and item_type. The list_type parameter is organized as follows: {Type::List, Type::[ITEM_TYPE]}.

Parameter(std::string_view name, std::pair<Type, Type> list_type)

Creates an optional list parameter with the given name, item_type, and default_value. The list_type parameter is organized as follows: {Type::List, Type::[ITEM_TYPE]}.

Parameter(std::string_view name, std::pair<Type, Type> list_type, Value default_value)

Member variables

Return

Represents a procedure/function return value. Values are defined by their name and type.

Constructors

Creates a return value with the given name and type.

Return(std::string_view name, Type type)

Creates a return value with the given name and list_type. The list_type parameter is organized as follows: {Type::List, Type::[ITEM_TYPE]}.

Return(std::string_view name, std::pair<Type, Type> list_type)

Member variables

RecordFactory

Factory class for Record.

Constructors

explicit RecordFactory(mgp_result *result)

Member functions

NewRecord

Adds a new result record.

  Record NewRecord() const

SetErrorMessage

Sets the given error message.

  void SetErrorMessage(std::string_view error_msg) const

  void SetErrorMessage(const char *error_msg) const

Record

Represents a record - the building block of Cypher procedure results. Each result is a stream of records, and a function’s record is a sequence of (field name: output value) pairs.

Constructors

explicit Record(mgp_result_record *record)

Member functions

Insert

Inserts a value of given type under field field_name.

  void Insert(const char *field_name, bool value)

  void Insert(const char *field_name, std::int64_t value)

  void Insert(const char *field_name, double value)

  void Insert(const char *field_name, std::string_view value)

  void Insert(const char *field_name, const char *value)

  void Insert(const char *field_name, const List &value)

  void Insert(const char *field_name, const Map &value)

  void Insert(const char *field_name, const Node &value)

  void Insert(const char *field_name, const Relationship &value)

  void Insert(const char *field_name, const Path &value)

  void Insert(const char *field_name, const Date &value)

  void Insert(const char *field_name, const LocalTime value)

  void Insert(const char *field_name, const LocalDateTime value)

  void Insert(const char *field_name, const Duration value)

  void Insert(const char *field_name, const Value &value)

Result

Represents a result - the single return value of a Cypher function.

Constructors

explicit Result(mgp_func_result *result)

Member functions

SetValue

Sets a return value of given type.

  void SetValue(bool value)

  void SetValue(std::int64_t value)

  void SetValue(double value)

  void SetValue(std::string_view value)

  void SetValue(const char *value)

  void SetValue(const List &value)

  void SetValue(const Map &value)

  void SetValue(const Node &value)

  void SetValue(const Relationship &value)

  void SetValue(const Path &value)

  void SetValue(const Date &value)

  void SetValue(const LocalTime &value)

  void SetValue(const LocalDateTime &value)

  void SetValue(const Duration &value)

SetErrorMessage

Sets the given error message.

  void SetErrorMessage(std::string_view error_msg) const

  void SetErrorMessage(const char *error_msg) const

Graph API

This section covers the interface for working with the Memgraph DB graph using the C++ API. A description of data types is available in the reference guide.

Graph

Constructors

explicit Graph(mgp_graph *graph)

Member functions

Order

Returns the graph order (number of nodes).

int64_t Order() const

Size

Returns the graph size (number of relationships).

int64_t Size() const

Nodes (GraphNodes)

Returns an iterable structure of the graph’s nodes.

GraphNodes Nodes() const

Relationships

Returns an iterable structure of the graph’s relationships.

GraphRelationships Relationships() const

GetNodeById

Returns the graph node with the given ID.

Node GetNodeById(Id node_id) const

ContainsNode

Returns whether the graph contains a node with the given ID.

bool ContainsNode(Id node_id) const

Returns whether the graph contains the given node.

bool ContainsNode(const Node &node) const

ContainsRelationship

bool ContainsRelationship(Id relationship_id) const

bool ContainsRelationship(const Relationship &relationship) const

IsMutable

Returns whether the graph is mutable.

bool IsMutable() const

IsTransactional

Returns whether the graph is in a transactional storage mode.

bool IsTransactional() const

CreateNode

Creates a node and adds it to the graph.

Node CreateNode();

DeleteNode

Deletes a node from the graph.

void DeleteNode(const Node &node)

DetachDeleteNode

Deletes a node and all its incident edges from the graph.

void DetachDeleteNode(const Node &node)

CreateRelationship

Creates a relationship of type type between nodes from and to and adds it to the graph.

Relationship CreateRelationship(const Node &from, const Node &to, std::string_view type)

DeleteRelationship

Deletes a relationship from the graph.

void DeleteRelationship(const Relationship &relationship)

SetFrom

Changes the from (start) node of the given relationship.

void SetFrom(Relationship &relationship, const Node &new_from)

SetTo

Changes the to (end) node of the given relationship.

void SetTo(Relationship &relationship, const Node &set_to)

ChangeType

Changes the relationship type

void ChangeType(Relationship &relationship, std::string_view new_type);

GraphNodes

Auxiliary class providing an iterable view of the nodes contained in the graph. GraphNodes values may only be used for iteration to obtain the values stored within.

Constructors

explicit GraphNodes(mgp_vertices_iterator *nodes_iterator)

Member variables

Member functions

GraphRelationships

Auxiliary class providing an iterable view of the relationships contained in the graph. GraphRelationships values may only be used for iteration to obtain the values stored within.

Constructors

explicit GraphRelationships(mgp_graph *graph)

Member variables

Member functions

Node

Represents a node (vertex) of the Memgraph graph.

Constructors

Creates a Node from the copy of the given mgp_vertex.

explicit Node(mgp_vertex *ptr)
explicit Node(const mgp_vertex *const_ptr)

Copy and move constructors:

Node(const Node &other) noexcept
Node(Node &&other) noexcept

Member functions

IsDeleted

Returns whether the node has been deleted.

bool IsDeleted() const

Id

Returns the node’s ID.

mgp::Id Id() const

Labels

Returns an iterable & indexable structure of the node’s labels.

class Labels Labels() const

HasLabel

Returns whether the node has the given label.

bool HasLabel(std::string_view label) const

Properties

Returns an iterable & indexable structure of the node’s properties.

std::unordered_map<std::string, mgp::Value> Properties() const

GetProperty

Gets value of node's property.

mgp::value GetProperty(const std::string& property) const

SetProperty

Sets the value of the node's property.

void SetProperty(std::string key, std::string value)

SetProperties

Updates the node's properties with the given map.

void SetProperties(std::unordered_map<std::string_view, Value> properties)

RemoveProperty

Removes the node's property.

void RemoveProperty(std::string property)

InRelationships

Returns an iterable structure of the node’s inbound relationships.

Relationships InRelationships() const

OutRelationships

Returns an iterable structure of the node’s outbound relationships.

Relationships OutRelationships() const

AddLabel

Adds a label to the node.

void AddLabel(std::string_view label)

RemoveLabel

Removes a label from a node.

void RemoveLabel(std::string_view label)

InDegree

Returns the in degree of a node.

size_t InDegree() const

OutDegree

Returns the out degree of a node.

size_t OutDegree() const

ToString

Returns the node's string representation, which has this format: "(id: node_id, labels: node_labels, properties: node_properties_map)".

std::string ToString() const

Operators

operator[]

Returns the value of the node’s property_name property.

Value operator[](std::string_view property_name) const

Relationship

Represents a relationship (edge) of the Memgraph graph.

Constructors

Creates a Relationship from the copy of the given mgp_edge.

explicit Relationship(mgp_edge *ptr)
explicit Relationship(const mgp_edge *const_ptr)

Copy and move constructors:

Relationship(const Relationship &other) noexcept
Relationship(Relationship &&other) noexcept

Member functions

IsDeleted

Returns whether the relationship has been deleted.

bool IsDeleted() const

Id

Returns the relationship’s ID.

mgp::Id Id() const

Type

Returns the relationship’s type.

std::string_view Type() const

Properties

Returns an iterable & indexable structure of the relationship’s properties.

std::unordered_map<std::string, mgp::Value> Properties() const

GetProperty

Gets value of the relationship's property.

mgp::value GetProperty(const std::string& property) const

SetProperty

Sets the value of the relationship's property.

void SetProperty(std::string key, std::string value)

SetProperties

Updates the relationship's properties with the given map.

void SetProperties(std::unordered_map<std::string_view, Value> properties)

RemoveProperty

Removes the relationship's property.

void RemoveProperty(std::string property)

From

Returns the relationship’s source node.

Node From() const

To

Returns the relationship’s source node.

Node To() const

ToString

Returns the relationship's string representation, which has this format: "(node_from.ToString())-(type: relationship_type, id: relationship_id, properties: relationship_properties_map)->(node_to.ToString())".

std::string ToString() const

Operators

operator[]

Returns the value of the relationship’s property_name property.

Value operator[](std::string_view property_name) const

Object is hashable using

std::hash<mgp::Relationship>

Relationships

Auxiliary class providing an iterable view of the relationships adjacent to a node. Relationships values may only be used for iteration to obtain the values stored within.

Constructors

explicit Relationships(mgp_edges_iterator *relationships_iterator)

Member variables

Member functions

Id

Represents the unique ID possessed by all Memgraph nodes and relationships.

Member functions

FromUint

Constructs an Id object from uint64_t.

static Id FromUint(uint64_t id)

FromInt

Constructs an Id object from int64_t.

static Id FromInt(int64_t id)

AsUint

Returns the ID value as uint64_t.

int64_t AsUint() const

AsInt

Returns the ID value as int64_t.

int64_t AsInt() const

Operators

Labels

Represents a view of node labels.

Constructors

explicit Labels(mgp_vertex *node_ptr)

Copy and move constructors:

Labels(const Labels &other) noexcept
Labels(Labels &&other) noexcept

Member variables

Member functions

Size

Returns the number of the labels, i.e. the size of their list.

size_t Size() const

Operators

operator[]

Returns the node’s label at position index.

std::string_view operator[](size_t index) const

Date

Represents a date with a year, month, and day.

Constructors

Creates a Date object from the copy of the given mgp_date.

explicit Date(mgp_date *ptr)
explicit Date(const mgp_date *const_ptr)

Creates a Date object from the given string representing a date in the ISO 8601 format (YYYY-MM-DD, YYYYMMDD, or YYYY-MM).

explicit Date(std::string_view string)

Creates a Date object with the given year, month, and day properties.

Date(int year, int month, int day)

Copy and move constructors:

Date(const Date &other) noexcept
Date(Date &&other) noexcept

Member functions

Now

Returns the current Date.

static Date Now()

Year

Returns the date’s year property.

int Year() const

Month

Returns the date’s month property.

int Month() const

Day

Returns the date’s day property.

int Day() const

Timestamp

Returns the date’s timestamp (microseconds since Unix epoch).

int64_t Timestamp() const

ToString

Returns the date's string representation, which has this format: "year-month-day".

std::string ToString() const

Operators

operator-

Date operator-(const Duration &dur) const

Duration operator-(const Date &other) const

operator[]

Returns the value of the relationship’s property_name property.

Value operator[](std::string_view property_name) const

Object is hashable using

std::hash<mgp::Date>

LocalTime

Represents a time within the day without timezone information.

Constructors

Creates a LocalTime object from the copy of the given mgp_local_time.

explicit LocalTime(mgp_local_time *ptr)
explicit LocalTime(const mgp_local_time *const_ptr)

Creates a LocalTime object from the given string representing a date in the ISO 8601 format ([T]hh:mm:ss, [T]hh:mm, [T]hhmmss, [T]hhmm, or [T]hh).

explicit LocalTime(std::string_view string)

Creates a LocalTime object with the given hour, minute, second, millisecond, and microsecond properties.

LocalTime(int hour, int minute, int second, int millisecond, int microsecond)

Copy and move constructors:

LocalTime(const LocalTime &other) noexcept
LocalTime(LocalTime &&other) noexcept

Member functions

Now

Returns the current LocalTime.

static LocalTime Now()

Hour

Returns the object’s hour property.

int Hour() const

Minute

Returns the object’s minute property.

int Minute() const

Second

Returns the object’s second property.

int Second() const

Millisecond

Returns the object’s millisecond property.

int Millisecond() const

Microsecond

Returns the object’s microsecond property.

int Microsecond() const

Timestamp

Returns the object’s timestamp (microseconds since Unix epoch).

int64_t Timestamp() const

ToString

Returns the object's string representation, which has this format: "hour:minute:second,microsecond milisecond".

std::string ToString() const

Operators

operator-

LocalTime operator-(const Duration &dur) const

Duration operator-(const LocalDateTime &other) const

Object is hashable using

std::hash<mgp::LocalTime>

LocalDateTime

Temporal type representing a date and a local time.

Constructors

Creates a LocalDateTime object from the copy of the given mgp_local_date_time.

explicit LocalDateTime(mgp_local_date_time *ptr)
explicit LocalDateTime(const mgp_local_date_time *const_ptr)

Creates a LocalDateTime object from the given string representing a date in the ISO 8601 format (YYYY-MM-DDThh:mm:ss, YYYY-MM-DDThh:mm, YYYYMMDDThhmmss, YYYYMMDDThhmm, or YYYYMMDDThh).

explicit LocalDateTime(std::string_view string)

Creates a LocalDateTime object with the given year, month, day, hour, minute, second, millisecond, and microsecond properties.

LocalDateTime(int year, int month, int day, int hour, int minute, int second, int millisecond, int microsecond)

Copy and move constructors:

LocalDateTime(const LocalDateTime &other) noexcept
LocalDateTime(LocalDateTime &&other) noexcept

Member functions

Now

Returns the current LocalDateTime.

static LocalDateTime Now()

Year

Returns the object’s year property.

int Year() const

Month

Returns the object’s month property.

int Month() const

Day

Returns the object’s day property.

int Day() const

Hour

Returns the object’s hour property.

int Hour() const

Minute

Returns the object’s minute property.

int Minute() const

Second

Returns the object’s second property.

int Second() const

Millisecond

Returns the object’s millisecond property.

int Millisecond() const

Microsecond

Returns the object’s microsecond property.

int Microsecond() const

Timestamp

Returns the date’s timestamp (microseconds since Unix epoch).

int64_t Timestamp() const

ToString

Returns the object's string representation, which has this format: "year-month-dayThour:minute:second,microsecond milisecond".

std::string ToString() const

Operators

operator-

LocalDateTime operator-(const Duration &dur) const

Duration operator-(const LocalDateTime &other) const

Object is hashable using

std::hash<mgp::LocalDateTime>

Duration

Represents a period of time in Memgraph.

Constructors

Creates a Duration object from the copy of the given mgp_duration.

explicit Duration(mgp_duration *ptr)
explicit Duration(const mgp_duration *const_ptr)

Creates a Duration object from the given string in the following format: P[nD]T[nH][nM][nS], where (1) n stands for a number, (2) capital letters are used as a separator, (3) each field in [] is optional, and (4) only the last field may be a non-integer.

explicit Duration(std::string_view string)

Creates a Duration object from the given number of microseconds.

explicit Duration(int64_t microseconds)

Creates a Duration object with the given day, hour, minute, second, millisecond, and microsecond properties.

Duration(double day, double hour, double minute, double second, double millisecond, double microsecond)

Copy and move constructors:

Duration(const Duration &other) noexcept
Duration(Duration &&other) noexcept

Member functions

Microseconds

Returns the duration as microseconds.

int64_t Microseconds() const

ToString

Returns the duration's string representation, which has this format: "microseconds ms".

std::string ToString() const

Operators

operator-

Duration operator-(const Duration &other) const

Duration operator-() const

Object is hashable using

std::hash<mgp::Duration>

Path

A path is a data structure consisting of alternating nodes and relationships, with the start and end points of a path necessarily being nodes.

Constructors

Creates a Path from the copy of the given mgp_path.

explicit Path(mgp_path *ptr)
explicit Path(const mgp_path *const_ptr)

Creates a Path starting with the given start_node.

explicit Path(const Node &start_node)

Copy and move constructors:

Path(const Path &other) noexcept
Path(Path &&other) noexcept

Member functions

ContainsDeleted

Returns whether the path contains any deleted nodes or relationships.

bool ContainsDeleted() const

Length

Returns the path length (number of relationships).

size_t Length() const

GetNodeAt

Returns the node at the given index. The index must be less than or equal to length of the path.

Node GetNodeAt(size_t index) const

GetRelationshipAt

Returns the relationship at the given index. The index must be less than the length of the path.

Relationship GetRelationshipAt(size_t index) const

Expand

Adds a relationship continuing from the last node on the path.

void Expand(const Relationship &relationship)

Pop

Removes the last node and the last relationship from the path.

void Pop()

ToString

Returns the path's string representation, which has nearly the same format as Relationship.ToString(), the difference being that Path.ToString() can have multiple nodes and relationships in its string representation, for example: "(node)-(relationship)->(node)-(relationship)->(node)...".

std::string ToString() const

Operators

Object is hashable using

std::hash<mgp::Path>

List

A list containing any number of values of any supported type.

Constructors

Creates a List from the copy of the given mgp_list.

explicit List(mgp_list *ptr)
explicit List(const mgp_list *const_ptr)

Creates an empty List.

explicit List()

Creates a List with the given capacity.

explicit List(size_t capacity)

Creates a List from the given vector.

explicit List(const std::vector<Value> &values)
explicit List(std::vector<Value> &&values)

Creates a List from the given initializer_list.

explicit List(std::initializer_list<Value> list)

Copy and move constructors:

List(const List &other) noexcept
List(List &&other) noexcept

Member variables

Member functions

ContainsDeleted

Returns whether the path contains any deleted values (Node, Relationship, or containers holding them).

bool ContainsDeleted() const

Size

Returns the size of the list.

size_t Size() const

Empty