Normally, MongoDB Collections are defined like this:
DuckbilledPlatypi = new Mongo.Collection("duckbilledplatypi");
I want to, though, dynamically generate Collections based on user input. For example, I might want it to be:
RupertPupkin20151212_20151218 = new Mongo.Collection("rupertPupkin20151212_20151218");
It would be easy enough to build up the Collection name:
var dynCollName = username + begindate +'_'+ enddate;
...and then pass "dynCollName") to Mongo.Collection:
= new Mongo.Collection(dynCollName);
...but what about the Collection instance name - how can that be dynamically generated? I would need something like:
"RupertPupkin20151212_20151218".ToRawName() = new Mongo.Collection(dynCollName);
-or:
"RupertPupkin20151212_20151218".Unstringify() = new Mongo.Collection(dynCollName);
...but AFAIK, there's no such thing...
On a single client instance, yes, and you could dynamically reference it. However in the general case (using it to sync data between the server and all connected clients), no.
I address this point in the Dynamically created collections section of common mistakes in a little detail, but the fundamental problem is that it would be highly complex to get all connected clients to agree on a dynamically generated set of collections.
It's much more likely that a finite set of collections where some have a flexible schema, is actually what you want. As Andrew Mao points out in the answer to this related question, partitioner is another tool available to help address some cases which give rise to this question.
Related
This question seemed fool at first sight for me, but then I realized that I don't have a proper answer yet, and interestingly also didn't find good explanation about it in my searches.
I'm new to Domain Driven Design concepts, so, even if the question is basic, feel free to add any considerations to it.
I'm designing in Rest API to configure Server Instances, and I came up with a Aggregate called Instance that contains a List of Configurations, only one specific Configuration will be active at a given time.
To add a Configuration, one would call an endpoint POST /instances/{id}/configurations with the body on the desired configuration. In response, if all okay, it would receive a HTTP 204 with a Header Location containing the new Configuration ID.
I'm planning to have only one Controller, InstanceController, that would call InstanceService that would manipulate the Instance Aggregate and then store to the Repo.
Since the ID's are generated by the repository, If I call Instance.addConfiguration and then InstanceRepository.store, how would I get the ID of the newly created configuration? I mean, it's a List, so It's not trivial as calling Instance.configuration.identity
A option would implement a method in Instance like, getLastAddedConfiguration, but this seems really brittle.
What is the general approach in this situation?
the ID's are generated by the repository
You could remove this extra complexity. Since Configuration is an entity of the Instance aggregate, its Id only needs to be unique inside the aggregate, not across the whole application. Therefore, the easiest is that the Aggregate assigns the ConfigurationId in the Instance.addConfiguration method (as the aggregate can easily ensure the uniqueness of the new Id). This method can return the new ConfigurationId (or the whole object with the Id if necessary).
What is the general approach in this situation?
I'm not sure about the general approach, but in my opinion, the sooner you create the Ids the better. For Aggregates, you'd create the Id before storing it (maybe a GUID), for entities, the Aggregate can create it the moment of creating/adding the entity. This allows you to perform other actions (eg publishing an event) using these Ids without having to store and retrieve the Ids from the DB, which will necessarily have an impact on how you implement and use your repositories and this is not ideal.
I'm rewriting an API to be more RESTful, but I'm struggling with a design issue. I'll explain the situation first and then my question.
SITUATION:
I have two sets resources users and items. Each user has a list of item, so the resource path would like something like this:
api/v1/users/{userId}/items
Also each user has an isPrimary property, but only one user can be primary at a time. This means that if I want to get the primary user you'd do something like this:
api/v1/users?isPrimary=true
This should return a single "primary" user.
I have client of my API that wants to get the items of the primary user, but can't make two API calls (one to get the primary user and the second to get the items of the user, using the userId). Instead the client would like to make a single API call.
QUESTION:
How should I got about designing an API that fetches the items of a single user in only one API call when all the client has is the isPrimary query parameter for the user?
MY THOUGHTS:
I think I have a some options:
Option 1) api/v1/users?isPrimary=true will return the list of items along with the user data.
I don't like this one, because I have other API clients that call api/v1/users or api/v1/users?isPrimary=true to only get and parse through user data NOT item data. A user can have thousands of items, so returning those items every time would be taxing on both the client and the service.
Option 2) api/v1/users/items?isPrimary=true
I also don't like this because it's ugly and not really RESTful since there is not {userId} in the path and isPrimary isn't a property of items.
Option 3) api/v1/users?isPrimary=true&isShowingItems=true
This is like the first one, but I use another query parameter to flag whether or not to show the items belonging to the user in the response. The problem is that the query parameter is misleading because there is no isShowingItems property associated with a user.
Any help that you all could provide will be greatly appreciated. Thanks in advance.
There's no real standard solution for this, and all of your solutions are in my mind valid. So my answer will be a bit subjective.
Have you looked at HAL for your API format? HAL has a standard way to embed data from one resources into another (using _embedded) and it sounds like a pretty valid use-case for this.
The server can decide whether to embed the items based on a number of criteria, but one cheap solution might be to just add a query parameter like ?embed=items
Even if you don't use HAL, conceptually you could still copy this behavior similarly. Or maybe you only use _embedded. At least it's re-using an existing idea over building something new.
Aside from that practical solution, there is nothing in un-RESTful about exposing data at multiple endpoints. So if you created a resource like:
/v1/primary-user-with-items
Then this might be ugly and inconsistent with the rest of your API, but not inherently
'not RESTful' (sorry for the double negative).
You could include a List<User.Fieldset> parameter called fieldsets, and then include things if they are specified in fieldsets. This has the benefit that you can reuse the pattern by adding fieldsets onto any object in your API that has fields you might wish to include.
api/v1/users?isPrimary=true&fieldsets=items
We are working on an app and need to be able to create new Mongo collections on the fly. Currently we have code such as this:
#Global = new Meteor.Collection('global')
We have a document in this mongo collections that looks like this:
{ "title" : "room_list", "room_list" : ['chat1', 'chat2'], ... }
Now I want to set up some type of loop or construct that would basically create the following
#chat1 = new Meteor.Collection('chat1')
#chat2 = new Meteor.Collection('chat2')
We are seeming to need this type of functionality to be able to create new collections of data on the fly.
We are looking into some type of dynamic variable declaration or is there a better way to dynamically create new meteor collections?
In most instances, you probably don't want to create multiple collections, but instead use one collection and send views of it to clients depending on their subscription.
You may want to check out the https://github.com/mizzao/meteor-partitioner package I've built which is designed especially for this purpose, and includes an example for how to do this for multiple chat rooms. You can also see https://github.com/mizzao/CrowdMapper for an implemented example.
I have a physician graph that looks something like this:
The query I use to get data from a WebApi backend looks like this:
var query = new breeze.EntityQuery().from("Physicians")
.expand("ContactInfo")
.expand("ContactInfo.Phones")
.expand("ContactInfo.Addresses")
.expand("PhysicianNotes")
.expand("PhysicianSpecialties")
.where("ContactInfo.LastName", "startsWith", lastInitial).take(5);
(note the ContactInfo is a pseudonym of the People object)
What I find is that If I request Contact.Phones to be expanded, I'll get just phones and no Notes or Specialties. If I comment out the phones I'll get Contact.Addresses and no other collections. If I comment out ContactInfo along with Phones and Addresses I'll get Notes only etc. Essentially, it seems like I can only get one collection at a time.
So, Is this a built in 'don't let the programmer shoot himself in the foot'?? safeguard or do I have to enable something?
OR is this graph too complicated?? should I consider a NoSql object store??
Thanks
You need to put all your expand clauses in a single one like this:
var query = new breeze.EntityQuery().from("Physicians")
.expand("ContactInfo, ContactInfo.Phones, ContactInfo.Addresses, PhysicianNotes, PhysicianSpecialties")
.where("ContactInfo.LastName", "startsWith", lastInitial).take(5);
You can see the documentation here: http://www.breezejs.com/sites/all/apidocs/classes/EntityQuery.html#method_expand
JY told you HOW. But BEWARE of performance consequences ... both on the data tier and over the wire. You can die a miserable death by grabbing too widely and deeply at once.
I saw the take(5) in his sample. That is crucial for restraining a runaway request (something you really must do also on the server). In general, I would reserve extended graph fetches of this kind for queries that pulled a single root entity. If I'm presenting a list for selection and I need data from different parts of the entity graph, I'd use a projection to get exactly what I need to display (assuming, of course, that there is no SQL View readily available for this purpose).
If any of the related items are reference lists (color, status, states, ...), consider bringing them into cache separately in a preparation step. Don't include them in the expand; Breeze will connect them on the client to your queried entities automatically.
Finally, as a matter of syntax, you don't have to repeat the name of a segment. When you write "ContactInfo.Phones", you get both ContactInfos and Phones so you don't need to specify "ContactInfo" by itself.
The repository in the CommonDomain only exposes the "GetById()". So what to do if my Handler needs a list of Customers for example?
On face value of your question, if you needed to perform operations on multiple aggregates, you would just provide the ID's of each aggregate in your command (which the client would obtain from the query side), then you get each aggregate from the repository.
However, looking at one of your comments in response to another answer I see what you are actually referring to is set based validation.
This very question has raised quite a lot debate about how to do this, and Greg Young has written an blog post on it.
The classic question is 'how do I check that the username hasn't already been used when processing my 'CreateUserCommand'. I believe the suggested approach is to assume that the client has already done this check by asking the query side before issuing the command. When the user aggregate is created the UserCreatedEvent will be raised and handled by the query side. Here, the insert query will fail (either because of a check or unique constraint in the DB), and a compensating command would be issued, which would delete the newly created aggregate and perhaps email the user telling them the username is already taken.
The main point is, you assume that the client has done the check. I know this is approach is difficult to grasp at first - but it's the nature of eventual consistency.
Also you might want to read this other question which is similar, and contains some wise words from Udi Dahan.
In the classic event sourcing model, queries like get all customers would be carried out by a separate query handler which listens to all events in the domain and builds a query model to satisfy the relevant questions.
If you need to query customers by last name, for instance, you could listen to all customer created and customer name change events and just update one table of last-name to customer-id pairs. You could hold other information relevant to the UI that is showing the data, or you could simply hold IDs and go to the repository for the relevant customers in order to work further with them.
You don't need list of customers in your handler. Each aggregate MUST be processed in its own transaction. If you want to show this list to user - just build appropriate view.
Your command needs to contain the id of the aggregate root it should operate on.
This id will be looked up by the client sending the command using a view in your readmodel. This view will be populated with data from the events that your AR emits.