I am currently trying to test a piece of my code that runs a query on the datastore before putting in a new entity to ensure that duplicates are not created. The code I wrote works fine in the context of the app, but the tests I wrote for that methods are failing. It seems that I cannot access data put into the datastore through queries in the context of the testing package.
One possibility might lie in the output from goapp test which reads: Applying all pending transactions and saving the datastore. This line prints out after both the get and put methods are called (I verified this with log statements).
I tried closing the context and creating a new one for the different operations, but unfortunately that didn't help either. Below is a simple test case that Puts in an object and then runs a query on it. Any help would be appreciated.
type Entity struct {
Value string
}
func TestEntityQuery(t *testing.T) {
c, err := aetest.NewContext(nil)
if err != nil {
t.Fatal(err)
}
defer c.Close()
key := datastore.NewIncompleteKey(c, "Entity", nil)
key, err = datastore.Put(c, key, &Entity{Value: "test"})
if err != nil {
t.Fatal(err)
}
q := datastore.NewQuery("Entity").Filter("Value =", "test")
var entities []Entity
keys, err := q.GetAll(c, &entities)
if err != nil {
t.Fatal(err)
}
if len(keys) == 0 {
t.Error("No keys found in query")
}
if len(entities) == 0 {
t.Error("No entities found in query")
}
}
There is nothing wrong with your test code. The issue lies in the Datastore itself. Most queries in the HR Datastore are not "immediately consistent" but eventually consistent. You can read more about this in the Datastore documentation.
So basically what happens is that you put an entity into the Datastore, and the SDK's Datastore "simulates" the latency that you can observe in production, so if you run a query right after that (which is not an ancestor query), the query result will not include the new entity you just saved.
If you put a few seconds sleep between the datastore.Put() and q.GetAll(), you will see the test passes. Try it. In my test it was enough to sleep just 100ms, and the test always passed. But when writing tests for such cases, use the StronglyConsistentDatastore: true option as can be seen in JonhGB's answer.
You would also see the test pass without sleep if you'd use Ancestor queries because they are strongly consistent.
The way to do this is to force the datastore to be strongly consistent by setting up the context like this:
c, err := aetest.NewContext(&aetest.Options{StronglyConsistentDatastore: true})
if err != nil {
t.Fatal(err)
}
Now the datastore won't need any sleep to work, which is faster, and better practice in general.
Update: This only works with the old aetest package which was imported via appengine/aetest. It does not work with the newer aetest package which is imported with google.golang.org/appengine/aetest. App Engine has changed from using an appengine.Context to using a context.Context, and consequently the way that the test package now works is quite different.
To compliment #JohnGB's answer in the latest version of aetest, there are more steps to get a context with strong consistency. First create an instance, then create a request from that instance, which you can use to produce a context.
inst, err := aetest.NewInstance(
&aetest.Options{StronglyConsistentDatastore: true})
if err != nil {
t.Fatal(err)
}
defer inst.Close()
req, err := inst.NewRequest("GET", "/", nil)
if err != nil {
t.Fatal(err)
}
ctx := appengine.NewContext(req)
Related
I'm migrating my Golang AppEngine app to 1.12+, and I need to switch to cloud.google.com/go/datastore. It's not clear to me how to use it with AppEngine, could someone please verify my assumptions?
My assumption is that somewhere inside main() I can run (note the context.Background()):
db, err := datastore.NewClient(context.Background(), datastore.DetectProjectID)
if err != nil {
panic(err)
}
defer db.Close()
And then from my handlers I can use that db:
func blah(w http.ResponseWriter, r *http.Request) {
ctx := r.Context()
key := datastore.NameKey("blah", blah, nil)
db.Get(ctx, key, blah2)
}
Am I correct? Or do I need to run datastore.NewClient() separately from each web handler?
I run datastore.NewClient() for each web handler. I only do this once for each web handler and only if that code needs to use the datastore. Also, make sure that you Close() it at the end of your handler otherwise you'll leak memory.
As we know service (controller/usecase) layer is to handle business logic,
repo is to handle db queries
Right now I have:
func (s *OrderService) Create(order models.Order) (models.Order, error) {
...
user := models.User{
Contact: order.Address.Contact,
}
createdUser, err := s.UserRepo.Save(user)
// err handling...
order.User = user
createdOrder, err := s.OrderRepo.save(order)
// err handling...
return order, nil
}
// user_repo.go
func (repo *UserRepo) Save(user models.User) (models.User, error) {
err := repo.DB.Debug().Save(&user).Error
// err handing...
return user, nil
}
// order_repo.go
func (repo *OrderRepo) Save(order models.Order) (models.Order, error) {
err := repo.DB.Debug().Save(&order).Error
// err handing...
return order, nil
}
I want apply gorm db.Begin() transaction to become more flexible instead of my current code is too static.
So should I remove the gorm.DB repo but
i. passing in the gorm.DB through params??
tx := s.DB.Begin()
createdUser, err := s.UserRepo.Save(user, tx)
ii. or straight away running query in service layer?? (but it broke ddd design concept)
tx := s.DB.Begin()
createdUser, err := tx.Create(&user)
if err != nil {
tx.Rollback()
}
createdOrder, err := tx.Create(&order)
if err != nil {
tx.Rollback()
}
tx.Commit()
As per DDD, Transactions should not cross aggregate boundaries.
References:
https://martinfowler.com/bliki/DDD_Aggregate.html
Defining Aggregate Boundaries
If we have a need to update them in a transaction for some reason, you might wanna relook if they should be part of some Aggregate
While writing the repository for aggregate, you can neatly hide the transactions in the repository layer
I usually follow the following interface
// holds the business logic to modify the aggregate, provided by business layer
type AggregateUpdateFunction func (a *Aggregate) error
type Repository interface {
Create(ctx context.Context, aggregate *Aggregate)
Read(ctx context.Context, id string) *Aggregate
// starts a read-modify-write cycle internally in a transaction
Update(ctx context.Context, id string, updateFunc AggregateUpdateFunction) error
}
GORM calls should definitely stay abstracted away in storage layer. If you leak implementation details like transaction handle to business logic, storage layer will become tightly coupled with that particular implementation of storage.
In domain-driven world one should probably model interface of storage layer in such way that it has all operations business logic needs to operate with domain objects rather than basic operations underlying database offers (point is if you later switch from SQL database to S3 REST API the interface towards business logic will stay same). So instead (or on top) of OrderRepo.Save() I would also create OrderRepo.SaveAsNewUser() (Order, User, err) which will internally leverage database transaction.
I'm using https://github.com/DATA-DOG/go-sqlmock
and trying to mock a connection to a db.
Now, I need to mock a ping command (for load balancing purposes). However, I can't find any information about how to do that.
For example, I would like to write a test like this
db, mock, _ := sqlmock.New()
// ExpectPing does not exist, but it is there anything similar?
mock.ExpectPing().WillReturnError("mock error")
err := db.Ping()
if err==nil{
t.Fatal("there should have been an error")
}
in addition, I need to inject this mocked object into a function. let's say New(*sql.DB) that outputs a new structure. so it must be compatible with *sql.DB struct. for this reason, sqlmock seems a good choice. However, I've not found the way to mock the ping command.
it is there any way to do this using this library?
if not, is there any other database/sql mock library that could do the trick?
Update: As of Jan 6, 2020, this functionality has been added to go-sqlmock, and is included in the v1.4.0 release.
Original answer:
No, there is "nothing similar." The Ping and PingContext methods depend on the driver implementing the Pinger interface, so you can't mimic it by, for example, expecting a 'SELECT 1' or something.
There is already an issue requesting to add this. It seems to not have gotten much attention. I suspect creating a PR (which is probably about 3 lines of code) would greatly increase the chance of having that feature added.
If your goal is to make a Ping fail, you should be able to mimic that by connecting to an invalid DB endpoint (either with or without sqlmock).
You certainly can mock db itself:
type mockedDB struct {
*sql.DB
}
func (db *mockedDB) Ping() error {
return errors.New("not implemented")
}
func Example_mockedDB_Ping() {
db, _, _ := sqlmock.New()
defer db.Close()
mdb := mockedDB{db}
fmt.Println("mdb.Ping(): ", mdb.Ping())
// Output: mdb.Ping(): not implemented
}
but I don't understand what is the purpose of such experiment.
In the same way you can put mock into new type and define ExpectPing on it.
I needed to mock the Ping() functionality as well. This is how I solved it:
type mockDB struct {
ReturnError error
}
func (db *mockDB) Ping() error {
return db.ReturnError
}
func (db *mockDB) PingContext(ctx context.Context) error {
return db.ReturnError
}
// Pinger to be able to mock & ask just for a ping
type Pinger interface {
PingContext(ctx context.Context) error
Ping() error
}
// DatabasePingCheck returns a Check that validates connectivity to a database/sql.DB using Ping().
func DatabasePingCheck(pinger Pinger, timeout time.Duration) Check {
return func() error {
ctx, cancel := context.WithTimeout(context.Background(), timeout)
defer cancel()
if pinger == nil {
return fmt.Errorf("pinger is nil")
}
return pinger.PingContext(ctx)
}
}
I've got a test that follows the following structure:
var testInstance aetest.Instance // initialized by a TestMain
TestThing(t *testing.T) {
defer cleanupGoogleDatastore(t, testInstance)
// insert basic test fixtures
// insert some new records here
// test assertions, etc.
}
The cleanupGoogleDatastore method just runs a datastore Query for all entities of a specific entity kind, and then deletes them one by one. Source here:
func cleanupGoogleDatastore(t *testing.T, testInstance aetest.Instance) {
q := datastore.NewQuery("Order")
ctx := GetContext(t, testInstance)
scanner := q.Run(ctx)
for {
var o model.Order
key, err := scanner.Next(&o)
if err == datastore.Done {
return
}
if err != nil {
t.Fatal(err.Error())
}
err = datastore.Delete(ctx, key)
if err != nil {
t.Fatal(err.Error())
}
}
}
The problem I'm having is that records inserted after the "basic test fixtures" aren't deleted by this deferred cleanup statement.
If I change this test function to instead look like the following:
var testInstance aetest.Instance // initialized by a TestMain
TestThing(t *testing.T) {
defer cleanupGoogleDatastore(t, testInstance)
// insert basic test fixtures
// insert some new records here
defer cleanupGoogleDatastore(t, testInstance)
// note that I have to call it TWICE - just moving it here is not enough.
// test assertions, etc.
}
then the newly created records are also deleted at the end of the test. My understanding was that deferred functions are just called at the end of the original function scope, which would imply that the query wouldn't be constructed and run until the end of the test, but that doesn't seem to be the case here. It seems like the query is being constructed when the defer statement is called and then executed at the end of the test.
I've tried moving cleanupGoogleDatastore into a closure (e.g. defer func() { cleanupGoogleDatastore(t, testInstance }() and that didn't change anything.
I suspect that somehow this is a case of the function arguments being evaluated at the point where I call defer instead of when the function is invoked, but since both t and testInstance are pointers rather than direct values I'm not sure how that could be happening. There's no other evidence that the two values have changed. Printing out the fields of both structs at the different logical evaluation points doesn't reveal anything new.
What's going on here?
This turned out to be a deliberate property of the local App Engine Datastore stub, which returns weakly consistent queries by default. I was able to resolve this by changing the code for cleanupGoogleDatastore to rely on an ancestor query, which successfully found and then deleted all of the entities. An alternative approach would have been to set aetest.Instance to be strongly consistent, but I didn't want to force strongly consistent behavior on all of my tests - just this one.
I'm using this driver: https://github.com/denisenkom/go-mssqldb and on production with an Azure SQL Database Standard S3 level we are getting way too much ErrBadconn - driver: Bad connection returned.
How can I prevent or at least gracefully handle that. Here's some code to show how things are setup.
A typical database function call
package dal
var db *sql.DB
type Database struct{}
func (d Database) Open() {
newDB, err := sql.Open("mssql", os.Getenv("dbconnestion"))
if err != nil {
panic(err)
}
err = newDB.Ping()
if err != nil {
panic(err)
}
db = newDB
}
func (d Database) Close() {
db.Close()
}
// ... in another file
func (e *Entities) Add(entity Entity) (int64, error) {
stmt, err := db.Prepare("INSERT INTO Entities VALUES(?, ?)")
if err != nil {
return -1, err
}
defer stmt.Close()
result, err := stmt.Exec(entity.Field1, entity.Field2)
if err != nil {
return -1, err
}
return result.LastInsertId()
}
On a web api
func main() {
db := dal.Database{}
db.Open()
defer db.Close()
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
entities := &dal.Entites{}
id, err := entities.Add(dal.Entity{Field1: "a", Field2: "b"})
if err != nil {
// here all across my web api and other web package or cli cmd that uses the dal I'm getting random ErrBadConn
}
})
}
So in short, the dal package is shared across multiple Azure web apps and command line Go apps.
I cannot see a pattern, those errors, which are frequent and randomly occurring. We are using Bugsnag to log the errors from all our apps.
For completion, sometimes our Standard S3 limit of 200 concurrent connections is reached.
I've triple checked everywhere on the package that access the database, making sure that all sql.Rows were closed, all db.Prepare statement are closed. As and example here's how a typical query function looks like:
func (e *Entities) GetByID(id int64) ([]Entity, error) {
rows, err := db.Query("SELECT * FROM Entities WHERE ID = ?", id)
if err != nil {
return nil, err
}
defer rows.Close()
var results []Entity
for rows.Next() {
var r Entity
err := readEntity(rows, &r)
if err != nil {
return nil, err
}
results = append(results, r)
}
if err = rows.Err(); err != nil {
return nil, err
}
return results, nil
}
The readEntity is basically only doing Scan on the fields.
I don't think it's code related, unit tests run well locally. It's just once deployed to Azure after running for sometimes, the driver: Bad connection start to show up very frequently.
I've ran this query to try and see as suggested in this question: Azure SQL server max pool size was reached error
select * from sys.dm_exeC_requests
But I'm not exactly sure what should I be paying attention here.
Things I've did / made sure of.
As it's suggested, the database/sql should handle the connection pool, so having a global variable for the database connection should be fine.
Making sure sql.Rows and db.Prepare statement are closed everywhere.
Increased the Azure SQL level to S3.
There's an issue for the sql driver I'm using talking about Azure SQL making database connection is a bad state if they are idling for more thant 2 minutes.
https://github.com/denisenkom/go-mssqldb/issues/81
Does the way database/sql handle the connection pooling is in any way not working with the way Azure SQL Database are manage.
Is there a way to gracefully handle this? I know that C# / Entity Framework have a connection resiliency / retry logic for Azure SQL, is it for the similar reasons? How could I implement this without having to pass everywhere on my error handling? I mean I don't want to do something like this clearly:
if err == sql.ErrBadConn {
// close and re-open the global db object
// retry
}
This is certainly not my only option here?
Any help would be extremely welcome.
Thank you
I'm not seeing anywhere that you close your database. Best practice (in other languages - not positive about Go) is to close / deallocate / dereference the database object after use, to release the connection back into the pool. If you're running out of connection resources, you're being told that you need to release things. Holding the reference open means nobody else can use that connection, so it'll stay around until it gets recycled because it's timed out. This is why you're getting it intermittently, rather than consistently - it depends on having a certain number of connections taking place w/in a certain period of time.
Pierre,
How often do you run into these connection issues? I recommend you build retry logic to graciously fail from bad connections. Here is how you would do it with C#: https://azure.microsoft.com/en-us/documentation/articles/sql-database-develop-csharp-retry-windows/
If you still feel you need assistance, feel free to shoot me an email with your server name and database name at meetb#microsoft.com and we will get our team to look into this issue.
Cheers,
Meet