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Cratis

Use concepts with Neo4j in Cratis Arc

Strongly typed values travel through the graph as the primitives they wrap, the same way they do in MongoDB. You never unwrap a ConceptAs<T> to bind it or rebuild one from a row.

Parameters

Section titled “Parameters”

A ConceptAs<T> binds as its inner value, including inside lists and maps. GraphParameterConverter applies these rules to every parameter:

Value Bound as
A concept Its inner value, converted by the rules below
Guid Its string form, because the graph has no GUID type
An enum Its name
decimal double, because the graph has no decimal type
A list or a dictionary A list or a map with every value converted
Anything else Unchanged 
await graph.Query<GroupMember>(cypher, new { groupId = new GroupId(id) });   // binds the Guid's text

This is what Chronicle’s Neo4j sink stores, so an identity written from an event is found by the same parameter.

Results

Section titled “Results”

GraphRecordMapper builds the result type from the row. A concept property is created from the primitive the row holds, and:

  • a Guid is read from its string form;
  • an enum is read from its name, or its number;
  • the graph’s 64-bit integers are narrowed to int and the other numeric types the property asks for;
  • a list becomes an array, List<T>, IReadOnlyList<T> or IEnumerable<T>, with every element converted, so a list of concepts maps to a list of concepts;
  • a missing column leaves the property at its default.

The graph stores primitives and arrays of primitives only, so a property that holds an object cannot be written by a projection; return a node or a relationship from your query and let the mapper read its properties.

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