I am trying to wrap my head around the best way to approach this problem.
I am importing a file that contains bunch of users so I created a handler called
ImportUsersCommandHandler and my command is ImportUsersCommand that has List<User> as one of the parameters.
In the handler, for each user that I need to import I have to make sure that the UserType is valid, this is where the confusion comes in. I need to do a query against the database, to get list of all possible user types and than for each user I am importing, I want to verify that the user type id in the import matches one that is in the db.
I have 3 options.
Create a query GetUserTypesQuery and get the rest of this and then pass it on to the ImportUsersCommand as a list and verify inside the command handler
Call the GetUserTypesQuery from the command itself and not pass it (command calling another query)
Do not create a GetUsersTypeQuery and just do the query results within the command (still a query but no query/handler involved)
I feel like all these are dirty solutions and not the correct way to apply CQRS.
I agree option 1 sounds the best but would maybe suggest adding a pre handler to validate your input?
So ImportUsersCommandHandler deals with importing you data (and only that) and add a handler that runs before that validates (in your example, checks the user types and maybe other stuff) and bails out of it does not pass. So it queries the db, checks the usertypes and does whatever it needs to if it fails. Otherwise it just passes down to your business handler (ImportUsersCommandHandler).
I am used to using Mediatr in NET Core and this pattern works well (this is what we do) so sorry if this does not fit with your environment/setup!
Related
I'm trying to use MediatR and everything looks good but i'm not sure what is the proper way to reuse the commands.
For example if I have a TodoListEntity a command (CreateTodoListCommand).
Everything is clear for now but what if I want to reuse this command and trigger some different behaviour.
For example i have two Todo forms.
When the form is triggered from AdminController only save in database is triggered. That should be ok.
I have a second form that is triggered from UserController. When customer fills the form I want to be created a record in the database, save some other information in another database table, and send email to the customer.
What is the proper way to reuse CreateTodoListCommand and combine it with other commands?
Create new command CreateTodoListFromUserControllerCommand which contains something like this?
await _mediator.Send(new CreateTodoListCommand());
await _mediator.Send(new SaveTodoListAdditionalDataCommand());
await _mediator.Publish(new TodoListCreatedEventFromUserControllerHandler());
Or there is something better than this?
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
The title may not be as accurate, if someone finds a better one and can update it, please do so :)
I have a small CMS to edit users.
I'm using Zend Framework 2 + Doctrine 2.
I have a fieldset + form to add a user and (possibly) the same one to update them.
The User entity has the following fields:id, username, password, email.
The fieldset has two validators that check if the username and the email already exist.
Since I'm using the same to update the users, when I change for example the username of the user and keep the email the same, it throws an error that the "email exists" (which is normal due to the validator) and the same when I change the username and keep the email etc.
What I want is to avoid that behavior and make it so it checks them only when they are really changed/updated.
I thought of some ways, but I'm not sure what the "best" approach would be to this.
Hardcode the whole thing, by checking if the fields change and then do the validation (which makes the whole fieldset pretty much useless)
Make a function in the User entity that accepts an array with the new values, then compares them to the old ones and passes the changed ones to a "validation" function that returns the errors (which is mostly like the previous way, but I guess a bit more structured)
Write a validator and attach it to a new form which will query the db to check if the email/username exists and it's not already in use by the particular id, but I'm not quite sure on how to write it since I can't figure out how to pass the id and the field to the validator
I guess the 3rd one would be the best since it does 2 jobs at one time, by checking if the field changed and is not already in use by another user.
What do you suggest? How do you deal with that kind of scenario?
I can post any code that is needed, but I think this is more of a structural problem and that the code I used is too common and easy to figure out.
I'm trying to wrap my head around CQRS. I'm drawing from the code example provided here. Please be gentle I'm very new to this pattern.
I'm looking at a logon scenario. I like this scenario because it's not really demonstrated in any examples i've read. In this case I do not know what the aggregate id of the user is or even if there is one as all I start with is a username and password.
In the fohjin example events are always fired from the domain (if needed) and the command handler calls some method on the domain. However if a user logon is invalid I have no domain to call anything on. Also most, if not all of the base Command/Event classes defined in the fohjin project pass around an aggregate id.
In the case of the event LogonFailure I may want to update a LogonAudit report.
So my question is: how to handle commands that do not resolve to a particular aggregate? How would that flow?
public void Execute(UserLogonCommand command)
{
var user = null;//user looked up by username somehow, should i query the report database to resolve the username to an id?
if (user == null || user.Password != command.Password)
;//What to do here? I want to raise an event somehow that doesn't target a specific user
else
user.LogonSuccessful();
}
You should take into account that it most cases CQRS and DDD is suitable just for some parts of the system. It is very uncommon to model entire system with CQRS concepts - it fits best to the parts with complex business domain and I wouldn't call logging user in a particularly complex business scenario. In fact, in most cases it's not business-related at all. The actual business domain starts when user is already identified.
Another thing to remember is that due to eventual consistency it is extremely beneficial to check as much as we can using only query-side, without event creating any commands/events.
Assuming however, that the information about successful / failed user log-ins is meaningful I'd model your scenario with following steps
User provides name and password
Name/password is validated against some kind of query database
When provided credentials are valid RegisterValidUserCommand(userId) is executed which results in proper event
If provided credentials are not valid
RegisterInvalidCredentialsCommand(providedUserName) is executed which results in proper event
The point is that checking user credentials is not necessarily part of business domain.
That said, there is another related concept, in which not every command or event needs to be business - related, thus it is possible to handle events that don't need aggregates to be loaded.
For example you want to change data that is informational-only and in no way affects business concepts of your system, like information about person's sex (once again, assuming that it has no business meaning).
In that case when you handle SetPersonSexCommand there's actually no need to load aggregate as that information doesn't even have to be located on entities, instead you create PersonSexSetEvent, register it, and publish so the query side could project it to the screen/raport.
I have a complex reporting application that allows clients to login and view reports for their client data. There are several sections of the application where there are database calls, using various controllers. I need to make sure that client A doesn't get client B's information via header manipulation.
The system authenticates, and assignes them a clientID and roleID. If your roleID >1, that means you work for the company hosting the data, and you can see all client info. I want to create a catch-all that basically works like this:
if($roleID > 1) {
...send query to database
}else {
if(...does this query select a record with clientID other than my $auth->clientID){
do not execute query
}else {
execute query
}
}
The problem is, I want this to run for every query that goes to the server... how can I place this code as a "roadblock" between the application and the DB? I already use Zend_Profiler to look at queries, so I know it is somehow possible, but cannot discern this from the Profiler code...
I can always write an authentication function and pass selected queries that way, but this catch-all would be easier to implement across all of the calls and would be future proof. Any help is appreciated.
it's application design fault.
you shoud use 'service architecture' - the only one entry point for queries would be a service. and any checks inside it.
If this is something you want run on every query, I'd suggest extending Zend_Db_Select and overwrite either the query() or assemble() functions to add in your logic. You'll also want to add a way for it to be aware of your $auth object.
Another option is to extend your database adapter so you can intercept the queries directly. IMO, you should try and do this at the application level though.
Depending on your database server, you can put a trace on the DB side.
Here's an example for Oracle:
http://orafaq.com/wiki/SQL_Trace