Part 4— Goxfer: a story about pushing a transactions dataset online Preamble In , I’ve coded the collector program, putting cleaned data inside a instance.Now, it’s time to use the Buxfer’s APIs to put the whole dataset online! Collector — Part 3 MongoDB is a program that reads structured data from MongoDB and then pushes it online via . Goxfer Buxfer’s APIs Journey In this article, I cover the fourth part of this journey: Part 1: Introduction Part 2: Cleaner Part 3: Collector Part 4 (this part): Goxfer Part 5: Conclusions Setup This new program will be coded with GoLang: this means I need to build a custom docker image and to install any dependencies via , one of the best package manager for Go. glide Ok, let’s start with docker!First, I need to update the service to build the container image: setup-golang Then, build the image and get inside the container: $ docker-compose build setup-golang$ docker-compose run --rm setup-golang bash Goxfer needs some dependencies, like (the MongoDB driver for GoLang) and (a handful HTTP client): I’ve to get them with glide because it will trace them using lock files, very useful when it comes to restore the project on another system. mgo gorequest # from inside the setup-golang container$ glide create$ glide get github.com/parnurzeal/gorequest$ glide get gopkg.in/mgo.v2 With two new files are added to the project: glide create : it’s the glide manifest where all the dependencies are listed and marked with a fixed version, following the semantic versioning specs glide.yaml : it’s a lock file to ensure deterministic restore procedure glide.lock With the dependencies are downloaded inside the new local folder and added inside the glide.yaml and glide.lock files. glide get vendor Now, with docker-compose is possible to restore/initialise the project on any system: $ docker-compose run --rm setup-golang Goxfer: hands on! So, what does Goxfer have to do?Let’s define the program procedure: connect to MongoDB initialise Buxfer’s session retrieve Buxfer’s accounts list fetch transactions from the DB and build transactions’ bulks push transactions’ bulks online via Buxfer’s APIs I‘ve to forge it step by step. Database The very first thing I need to code is the database connection. is a MongoDB driver and it just need the database host to establish the connection, plus the database name and the name of the collection it will query for the transactions.I need to define those informations inside the as environment variables for the , already drafted in : mgo docker-compose.yml goxfer service Part 1 Great! Environment variables are always the best to configure things from outside, . as Twelve Factors App teaches Now, I’ve to use the mgo driver to connect to MongoDB.But first, I’ve got to get those env vars… will do it for me: os.Getenv It’s time to create the MongoDB connection and to get the transactions collection: The database connection is required by the next steps so I’ve to stop the program if this execution fails: will be fine. panic Buxfer’s session Buxfer requires an for each request performed; so, before proceeding, I’ve to establish a new session.I’ll use that is an HTTP client with a practical and easy-to-use interface.The requires a username and a password, so I’ve to put new environment variables inside the docker-compose.yml file: authentication token gorequest login API Then, I’ve to perform the HTTP request inside Goxfer: I’ve also defined the struct to store the login response, of course.Then, I’ve checked for lib and http errors: if everything’s fine, then I can use the token taken from the response. LoginResponse Accounts list Before proceeding with the transactions, I need to get the accounts list because later I will need the id of each account.So, for now, I just have to map the expense and the income accounts with their ids: Also here, I’ve used gorequest to perform the HTTP GET call.Buxfer’s APIs authentication is done through the session token so I’ve attached it to the querystring ( ).The response is then stored inside the custom struct : also this step is required by the next ones, so I’ve to panic if at least an error has occurred.If everything went fine, I can check the accounts list.I’ve got only two accounts, so the control can be exclusive. .Query(“token=” + token) AccountsListReponse Now, I need to update the docker-compose.yml file with and constants, so the code above won’t break: EXPENSE_ACCOUNT_BUXFER INCOME_ACCOUNT_BUXFER Great!Move on! Transactions’ bulks Now, what I want to do is to get all the transactions from MongoDB and then to push them on Buxfer.But, there’s a problem: Buxfer’s APIs are limited. In fact, it is possible to push just one transaction per time: Well, I don’t want to wait for the end of each request to perform a new one, neither to perform 1000 calls in parallel.So, I think I’ll go for pushing a per time.To do that, I need two things: https://www.buxfer.com/help/api#add_transaction bulk of 20 transactions pack the transactions inside a matrix ( (basically, array of arrays)) array of bulks (ab)use to perform HTTP calls in parallel GoLang’s goroutines Each bulk has a fixed size, defined by the environment variable , that I’m going to put inside the docker-compose.yml file: BULK_LENGTH And now, let’s define the procedure to get the transactions from the database and to populate the bulks matrix: At the beginning, transactions are stored inside the variable that is an array (a in GoLang) of (the transaction’s model).Then, I calculate the number of iterations to populate the transactions matrix, by dividing the length of the transactions’ list by BULK_LEN.The second iteration is done if the amount of transactions is not a multiple of BULK_LEN. results slice Transaction Pushing to Buxfer Ok, this is .As I said, I want to push bulks of 20 transactions per time. This means I’ve to launch and then wait until they have finished. All of them. Then, I can start with a new bulk and so on. the tough part 20 goroutines in parallel will help me handling concurrent goroutines execution: inside this package there’s the that basically provides three methods: sync WaitGroup : increment the workers counter Add : stop the main thread until the workers counter is equal to zero Wait : decrement the workers counter Done So, what I’ve to do is: loop through the bulks’ matrix then for each row (aka bulk) I’ve to increment the WaitGroup counter by adding the length of the bulk then I need to loop through the current bulk and for each transaction instantiate a new goroutine to push the data on Buxfer for each goroutine that has finished, I need to decrement the WaitGroup counter via the Done method eventually, I’ve to stop until the entire bulk has finished, using the Wait method of the WaitGroup, so the loop can continue with the next row of the matrix During this procedure, I want to store how many transactions have been added and how many haven’t. Later I’ll log this information. So, here’s the code, except for the actual request to Buxfer: Now, the last thing to code is the function.This will be a function that may return an error if something goes wrong while pushing the transaction online, following the way : addTransaction how GoLang treats errors like errors and not like exception Briefly: the HTTP request payload is composed by the following fields: : transaction’s description description : transaction’s amount amount : calculated matching the Buxfer accounts list, fetched previously accountId : transaction’s tags converted into a comma-separated string tags : date formatted with format date YYYY-MM-DD : session token token : transaction’s type, calculated the same way of accountId type Then the request is made and the response is stored inside the new struct : if no error occurred, it will return . AddResponseBody nil Putting everything altogether (on github because it is too long to be displayed here): https://github.com/wilk/from-csv-to-buxfer/blob/master/go/src/goxfer.go Run it, dude! The final step: launch it 🚀! $ docker-compose run --rm goxfer Yuppie 🎉 End of part 4 Wow, this last part was tough 😵It requires a lot of work and a lot of testing. In fact, initially the API for adding transactions on Buxfer was different ( ) and it got changed ( ) at the end of October. I had to change the source code, performing new tests with and before running the program safety. and bugged and fixed PostMan curl However, even if I tested everything beforehand, I got this: Nothing to say.I was aware of this flaw (in fact, I didn’t prepare any log to trace unpushed transactions) but I wanted to try anyway, putting all of my trust into manual testing I did earlier.That required me to manually search inside thousands of logs: it was quite painful but I deserved it, so it’s ok 😬 But now, 🎉I would like to spend more words about this part but I’ll do in the next part: ! I’ve all of my transactions of 2016 online on Buxfer Conclusions If you enjoyed this article don’t forget to share it!See you in ! Part 5: Conclusions Sources Source code is available here: https://github.com/wilk/from-csv-to-buxfer Update I’ve improved the unpushed transactions logs and I found that one of the raw transactions was corrupted: its date was so that’s why Buxfer refused to accept it.Anyway, Cleaner, Collector and Goxfer did the job and they did it really well! 29/11/1898

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