const ManagedRelationship(Symbol inversePropertyName, { ManagedRelationshipDeleteRule onDelete: ManagedRelationshipDeleteRule.nullify, bool isRequired: false })

Creates an instance of this type.

Source 

const ManagedRelationship(this.inversePropertyName,
    {this.onDelete: ManagedRelationshipDeleteRule.nullify,
    this.isRequired: false});