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CREATE EDGE

CREATE EDGE creates an edge type with the given name in a graph space.

OpenCypher compatibility

Edge types in nGQL are similar to relationship types in openCypher. But they are also quite different. For example, the ways to create them are different.

  • In openCypher, relationship types are created together with vertices in CREATE statements.
  • In nGQL, edge types are created separately using CREATE EDGE statements. Edge types in nGQL are more like tables in MySQL.

Prerequisites

Running the CREATE EDGE statement requires some privileges for the graph space. Otherwise, Nebula Graph throws an error.

Syntax

To create an edge type in a specific graph space, you must specify the current working space with the USE statement.

CREATE EDGE [IF NOT EXISTS] <edge_type_name>
    (
      <prop_name> <data_type> [NULL | NOT NULL] [DEFAULT <default_value>] [COMMENT '<comment>']
      [{, <prop_name> <data_type> [NULL | NOT NULL] [DEFAULT <default_value>] [COMMENT '<comment>']} ...] 
    )
    [TTL_DURATION = <ttl_duration>]
    [TTL_COL = <prop_name>]
    [COMMENT = '<comment>'];
Parameter Description
IF NOT EXISTS Detects if the edge type that you want to create exists. If it does not exist, a new one will be created. The edge type existence detection here only compares the edge type names (excluding properties).
<edge_type_name> The edge type name must be unique in a graph space. Once the edge type name is set, it can not be altered. The rules for permitted edge type names are the same as those for graph space names. For prohibited names, see Keywords and reserved words.
<prop_name> The name of the property. It must be unique for each edge type. The rules for permitted property names are the same as those for edge type names.
<data_type> Shows the data type of each property. For a full description of the property data types, see Data types and Boolean.
NULL \| NOT NULL Specifies if the property supports NULL | NOT NULL. The default value is NULL.
DEFAULT Specifies a default value for a property. The default value can be a literal value or an expression supported by Nebula Graph. If no value is specified, the default value is used when inserting a new edge.
COMMENT The remarks of a certain property or the edge type itself. The maximum length is 256 bytes. By default, there will be no comments on an edge type.
TTL_DURATION Specifies the life cycle for the property. The property that exceeds the specified TTL expires. The expiration threshold is the TTL_COL value plus the TTL_DURATION. The default value of TTL_DURATION is 0. It means the data never expires.
TTL_COL Specifies the property to set a timeout on. The data type of the property must be int or timestamp. An edge type can only specify one field as TTL_COL. For more information on TTL, see TTL options.

Examples

nebula> CREATE EDGE follow(degree int);

# The following example creates an edge type with no properties.
nebula> CREATE EDGE no_property();

# The following example creates an edge type with a default value.
nebula> CREATE EDGE follow_with_default(degree int DEFAULT 20);

# In the following example, the TTL of the p2 field is set to be 100 seconds.
nebula> CREATE EDGE e1(p1 string, p2 int, p3 timestamp) \
        TTL_DURATION = 100, TTL_COL = "p2";

Implementation of the operation

Trying to use a newly created edge type may fail because the creation of the edge type is implemented asynchronously.

Nebula Graph implements the creation of the edge type in the next heartbeat cycle. To make sure the creation is successful, take the following approaches:

  • Find the new edge type in the result of SHOW EDGES. If you cannot, wait a few seconds and try again.
  • Wait for two heartbeat cycles, i.e., 20 seconds.

To change the heartbeat interval, modify the heartbeat_interval_secs parameter in the configuration files for all services.

Last update: August 13, 2021
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