Data Types and Collections in PGX

Primitive Data Types

PGX supports the following primitive data types.

• Numeric Types: integer, long, float, and double. These types have the same size, range and precision of the corresponding Java primitive data type.
• Boolean Type: The boolean data type has only two possible values: true and false. As with Java and C++, its size is not precisely defined.
• String: String is a primitive data type in PGX. PGX follows the Java conventions for String representation.
• Datetime Types: date, time, timestamp, time with time zone, and timestamp with time zone. These types correspond to the Java types LocalDate, LocalTime, LocalDateTime, OffsetTime, OffsetDateTime from the standard library package java.util.time.
• Vertex and Edge: The type vertex or edge of the graph itself is a proper type in PGX.

An overview of the different data types and their integration in different languages and APIs is as follows:

All properties and scalar variables should be one of the above primitive data types.

Note that vertex (and edge) is itself a valid primitive data type. For instance, in a path-finding algorithm, each vertex can have a temporary property predecessor that stores which incoming neighbor is the predecessor vertex in the path. Such a property would have the type vertex.

Also note that in the graph config, local_date should be used instead of date.

To see examples of usage of datetime data types, see Using Datetime Data Types.

Data Type Limitations

The following table summarizes the minimum and maximum values for each data type. Note that for float and double types, the smallest absolute value is included in the table, the minimum value is the negative of maximum value for these types.

For string values, PGX supports arbitrary long strings.

Collections

PGX supports three different collection types: sequence, set and order. All of these collections can contain values of the vertex type, but each has different semantics regarding uniqueness and preserving the order of its elements:

• Sequence: a sequence works basically like a list. It preserves the order of the elements added to it, and the same element can appear multiple times.

• Set: a set can contain the same value once at the most. Adding a value that is already in the set will have no effect. set does not preserve the order of the elements it contains.

• Order: just like the set, the order collection will contain each element once at the most. But the order preserves the order of the elements inserted into it; i.e., it is a FIFO data structure.

To see examples of creation and usage of the different collections, see Using Collections.

Immutable Collections

Some operations, like PgxGraph.getVertices() and PgxGraph.getEdges() return immutable collections. These collections behave like normal collections, but cannot be modified by operations like addAll or removeAll and clear.

An immutable collection can be transformed into a mutable collection by using the toMutable method, which returns a mutable copy of the collection. If toMutable is called on a collection that is already mutable, the method has the same result as the method clone.

To check if a collection is mutable, the isMutable method can be used.

Maps

PGX provides two different kinds of maps:

• Graph-bound maps can hold mappings between types in PropertyType. This is the kind of maps to use if the key or value types are graph-related like VERTEX and EDGE otherwise using session-bound maps is recommended.
• Session-bound maps can map between non graph-related types and are directly bound to the session.

To see examples of creation and usage of maps, see Using Maps.