I am using GORM with Go and when I try to do an insert, it fails because GORM surrounds the table and column names with double quotes, and hence the insert statement becomes invalid. Relevant code is as follows:
type Record struct {
Company string `json:"-" gorm:"column:company"`
Category string `json:"-" gorm:"column:category"`
}
err := dm.postgresDB.Transaction(func(tx *gorm.DB) error {
if err := tx.Create(&rd).Error; err != nil {
I am not sure why this is happening. Any help would be appreciated. Thanks.
Related
I would like to know if there's any approach that would allow me to ignore null types while unmarshalling a MongoDB document into a Go struct.
Right now I have some auto-generate Go structs, something like this:
type User struct {
Name string `bson:"name"`
Email string `bson:"email"`
}
Changing the types declared in this struct is not an option, and here's the problem; in a MongoDB database, which I do not have total control, some of the documents have been inserted with null values were originally I was not expecting nulls. Something like this:
{
"name": "John Doe",
"email": null
}
As the string types declared inside my struct are not pointers, they can't receive a nil value, so whenever I try to unmarshall this document in my struct, it returns an error.
Preventing the insertion of this kind of document into the database would be the ideal solution, but for my use case, ignoring the null values would also be acceptable. So after unmarshalling the document my User instance would look like this
User {
Name: "John Doe",
Email: "",
}
I'm trying to find, either some annotation flag, or an option that could be passed to the method Find/FindOne, or maybe even a query parameter to prevent returning any field containing null values from the database. Without any success until now.
Are there any built-in solutions in the mongo-go-driver for this problem?
The problem is that the current bson codecs do not support encoding / decoding string into / from null.
One way to handle this is to create a custom decoder for string type in which we handle null values: we just use the empty string (and more importantly don't report error).
Custom decoders are described by the type bsoncodec.ValueDecoder. They can be registered at a bsoncodec.Registry, using a bsoncodec.RegistryBuilder for example.
Registries can be set / applied at multiple levels, even to a whole mongo.Client, or to a mongo.Database or just to a mongo.Collection, when acquiring them, as part of their options, e.g. options.ClientOptions.SetRegistry().
First let's see how we can do this for string, and next we'll see how to improve / generalize the solution to any type.
1. Handling null strings
First things first, let's create a custom string decoder that can turn a null into a(n empty) string:
import (
"go.mongodb.org/mongo-driver/bson/bsoncodec"
"go.mongodb.org/mongo-driver/bson/bsonrw"
"go.mongodb.org/mongo-driver/bson/bsontype"
)
type nullawareStrDecoder struct{}
func (nullawareStrDecoder) DecodeValue(dctx bsoncodec.DecodeContext, vr bsonrw.ValueReader, val reflect.Value) error {
if !val.CanSet() || val.Kind() != reflect.String {
return errors.New("bad type or not settable")
}
var str string
var err error
switch vr.Type() {
case bsontype.String:
if str, err = vr.ReadString(); err != nil {
return err
}
case bsontype.Null: // THIS IS THE MISSING PIECE TO HANDLE NULL!
if err = vr.ReadNull(); err != nil {
return err
}
default:
return fmt.Errorf("cannot decode %v into a string type", vr.Type())
}
val.SetString(str)
return nil
}
OK, and now let's see how to utilize this custom string decoder to a mongo.Client:
clientOpts := options.Client().
ApplyURI("mongodb://localhost:27017/").
SetRegistry(
bson.NewRegistryBuilder().
RegisterDecoder(reflect.TypeOf(""), nullawareStrDecoder{}).
Build(),
)
client, err := mongo.Connect(ctx, clientOpts)
From now on, using this client, whenever you decode results into string values, this registered nullawareStrDecoder decoder will be called to handle the conversion, which accepts bson null values and sets the Go empty string "".
But we can do better... Read on...
2. Handling null values of any type: "type-neutral" null-aware decoder
One way would be to create a separate, custom decoder and register it for each type we wish to handle. That seems to be a lot of work.
What we may (and should) do instead is create a single, "type-neutral" custom decoder which handles just nulls, and if the BSON value is not null, should call the default decoder to handle the non-null value.
This is surprisingly simple:
type nullawareDecoder struct {
defDecoder bsoncodec.ValueDecoder
zeroValue reflect.Value
}
func (d *nullawareDecoder) DecodeValue(dctx bsoncodec.DecodeContext, vr bsonrw.ValueReader, val reflect.Value) error {
if vr.Type() != bsontype.Null {
return d.defDecoder.DecodeValue(dctx, vr, val)
}
if !val.CanSet() {
return errors.New("value not settable")
}
if err := vr.ReadNull(); err != nil {
return err
}
// Set the zero value of val's type:
val.Set(d.zeroValue)
return nil
}
We just have to figure out what to use for nullawareDecoder.defDecoder. For this we may use the default registry: bson.DefaultRegistry, we may lookup the default decoder for individual types. Cool.
So what we do now is register a value of our nullawareDecoder for all types we want to handle nulls for. It's not that hard. We just list the types (or values of those types) we want this for, and we can take care of all with a simple loop:
customValues := []interface{}{
"", // string
int(0), // int
int32(0), // int32
}
rb := bson.NewRegistryBuilder()
for _, v := range customValues {
t := reflect.TypeOf(v)
defDecoder, err := bson.DefaultRegistry.LookupDecoder(t)
if err != nil {
panic(err)
}
rb.RegisterDecoder(t, &nullawareDecoder{defDecoder, reflect.Zero(t)})
}
clientOpts := options.Client().
ApplyURI("mongodb://localhost:27017/").
SetRegistry(rb.Build())
client, err := mongo.Connect(ctx, clientOpts)
In the example above I registered null-aware decoders for string, int and int32, but you may extend this list to your liking, just add values of the desired types to the customValues slice above.
You can go through the operator $exists and Query for Null or Missing Fields for a detail explanation.
In the mongo-go-driver, you can try below query:
The email => nil query matches documents that either contains the email field whose value is nil or that do not contain the email field.
cursor, err := coll.Find(
context.Background(),
bson.D{
{"email", nil},
})
You have to just add the $ne operator in the above query to get the records that do not have the field email or do not have the value nil in email. For more details about the operator $ne
If you know ahead of time which fields could potentially be null in your mongoDB records, you can use pointers in your structs instead:
type User struct {
Name string `bson:"name"` // Will still fail to decode if null in Mongo
Email *string `bson:"email"` // Will be nil in go if null in Mongo
}
Just remember that now you'll need to code more defensively around anything that uses this value after decoding from mongo, eg:
var reliableVal string
if User.Email != nil {
reliableVal = *user.Email
} else {
reliableVal = ""
}
I have a postgres db that I would like to generate tables for and write to using Gorp, however I get an error message when I try to insert due to the slices contained within my structs "sql: converting argument $4 type: unsupported type []core.EmbeddedStruct, a slice of struct.
My structs look as follows:
type Struct1 struct {
ID string
Name string
Location string
EmbeddedStruct []EmbeddedStruct
}
type EmbeddedStruct struct {
ID string
Name string
struct1Id string
EmbeddedStruct2 []EmbeddedStruct2
}
type EmbeddedStruct2 struct {
ID string
Name string
embeddedStructId string
}
func (repo *PgStruct1Repo) Write(t *core.Struct1) error {
trans, err := createTransaction(repo.dbMap)
defer closeTransaction(trans)
if err != nil {
return err
}
// Check to see if struct1 item already exists
exists, err := repo.exists(t.ID, trans)
if err != nil {
return err
}
if !exists {
log.Debugf("saving new struct1 with ID %s", t.ID)
err = trans.Insert(t)
if err != nil {
return err
}
return nil
}
return nil
}
Does anyone have any experience with/or know if Gorp supports inserting slices? From what I've read it seems to only support slices for SELECT statements
Gorp supports inserting a variadic number of slices, so if you have a slice records, you can do:
err = db.Insert(records...)
However, from your question it seems you want to save a single record that has a slice struct field.
https://github.com/go-gorp/gorp
gorp doesn't know anything about the relationships between your structs (at least not yet).
So, you have to handle the relationship yourself. The way I personally would solve this issue is to have Gorp ignore the slice on the parent:
type Struct1 struct {
ID string
Name string
Location string
EmbeddedStruct []EmbeddedStruct `db:"-"`
}
And then use the PostInsert hook to save the EmbeddedStruct (side note, this is a poor name as it is not actually an embedded struct)
func (s *Struct1) PostInsert(sql gorp.SqlExecutor) error {
for i := range s.EmbeddedStruct {
s.EmbeddedStruct[i].struct1Id = s.ID
}
return sql.Insert(s.EmbeddedStruct...)
}
And then repeat the process on EmbeddedStruct2.
Take care to setup the relationships properly on the DB side to ensure referential integrity (e.g. ON DELETE CASCADE / RESTRICT), and it would probably be a good idea to wrap the whole thing in a transaction.
I'm using go and the package uuid to generate a uuid of type [16]byte. However when I try to insert that uuid into my postgres column of type uuid I get the error converting argument $1 type: unsupported type [16]uint8, a array. So apparently I should convert the uuid on the client before I insert it into the db. How should I do that? What type should I convert it to?
In short: What go data type will work with uuid in postgres?
Thanks to the link from #sberry, I found success. Here are snippets of the code for your benefit (with a PostgreSQL 9.5 database):
import (
"database/sql"
"net/http"
"github.com/google/uuid"
)
type Thing struct {
ID uuid.UUID `json:"-" sql:",type:uuid"`
Name string `json:"name"`
}
// For a database table created as such:
// CREATE TABLE things (
// id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
// name TEXT DEFAULT ''::text
// )
func selectThingssSQL() ([]Thing, error) {
things := make([]Thing, 0)
rows, err := db.Query("SELECT id, name FROM things")
if err != nil {
return nil, err
}
defer rows.Close()
for rows.Next() {
t := &Thing{}
if err := rows.Scan(&t.ID, &t.Name); err != nil {
return nil, err
}
things = append(things, *t)
}
return things, nil
}
I have a small Go program which uses a a postgresql db. In it there is a query which can return no rows, and the code I'm using to deal with this isn't working correctly.
// Get the karma value for nick from the database.
func getKarma(nick string, db *sql.DB) string {
var karma int
err := db.QueryRow("SELECT SUM(delta) FROM karma WHERE nick = $1", nick).Scan(&karma)
var karmaStr string
switch {
case err == sql.ErrNoRows:
karmaStr = fmt.Sprintf("%s has no karma.", nick)
case err != nil:
log.Fatal(err)
default:
karmaStr = fmt.Sprintf("Karma for %s is %d.", nick, karma)
}
return karmaStr
}
This logic is taken directly from the Go documentation. When there are no rows corresponding to nick, the following error occurs:
2016/07/24 19:37:07 sql: Scan error on column index 0: converting driver.Value type <nil> ("<nil>") to a int: invalid syntax
I must be doing something stupid - clues appreciated.
I believe your issue is that you're getting a NULL value back from the database, which go translates into nil. However, you're scanning into an integer, which has no concept of nil. One thing you can do is scan into a type that implements the sql.Scanner interface (and can handle NULL values), e.g., sql.NullInt64.
In the example code in the documentation, I'd assume they have a NOT NULL constraint on the username column. I think the reason for this is because they didn't want to lead people to believe that you have to use NULL-able types across the board.
I reworked the code to get the results I wanted.
// Get the karma value for nick from the database.
func getKarma(nick string, db *sql.DB) string {
var karma int
rows, err := db.Query("SELECT SUM(delta) FROM karma WHERE nick = $1", nick)
if err != nil {
log.Fatal(err)
}
defer rows.Close()
karmaStr := fmt.Sprintf("%s has no karma.", nick)
if rows.Next() {
rows.Scan(&karma)
karmaStr = fmt.Sprintf("Karma for %s is %d.", nick, karma)
}
return karmaStr
}
Tempted to submit a documentation patch of some sort to the database/sql package.
I'm fairly new to both Go and MongoDB. Trying to select a single field from the DB and save it in an int slice without any avail.
userIDs := []int64{}
coll.Find(bson.M{"isdeleted": false}).Select(bson.M{"userid": 1}).All(&userIDs)
The above prints out an empty slice. However, if I create a struct with a single ID field that is int64 with marshalling then it works fine.
All I am trying to do is work with a simple slice containing IDs that I need instead of a struct with a single field. All help is appreciated.
Because mgo queries return documents, a few lines of code is required to accomplish the goal:
var result []struct{ UserID int64 `bson:"userid"` }
err := coll.Find(bson.M{"isdeleted": false}).Select(bson.M{"userid": 1}).All(&result)
if err != nil {
// handle error
}
userIDs := make([]int64, len(result))
for i := range result {
userIDs[i] = result.UserID
}