var filterBuilder = Builders<WorkflowInstance>.Filter;
var filter = filterBuilder.Eq("WorkflowCode", workflowCode)
& filterBuilder.Eq("InstanceStatus", "WIP")
& filterBuilder.ElemMatch("WorkflowStateInstanceList", Builders<WorkflowStateInstance>.Filter.ElemMatch("ApproverUserList", Builders<InstanceStateApprover>.Filter.Eq("ApproverUser", userID))
& Builders<WorkflowStateInstance>.Filter.Eq("StateStatus", "WIP"));
List<WorkflowInstance> listInstance = InstanceMongo.Collection.Find(filter).ToList();
注：WorkflowInstance/WorkflowStateInstance/InstanceStateApprover 为与Mongo对应的C#实体类