SchemaColumn.relationship(String name, ManagedPropertyType type, { bool isNullable: true, bool isUnique: false, String relatedTableName, String relatedColumnName, ManagedRelationshipDeleteRule rule: ManagedRelationshipDeleteRule.nullify })

A convenience constructor for properties that represent foreign key relationships.

Source 

SchemaColumn.relationship(this.name, ManagedPropertyType type,
    {this.isNullable: true,
    this.isUnique: false,
    this.relatedTableName,
    this.relatedColumnName,
    ManagedRelationshipDeleteRule rule: ManagedRelationshipDeleteRule.nullify}) {
  isIndexed = true;
  _type = typeStringForType(type);
  _deleteRule = deleteRuleStringForDeleteRule(rule);
}