I have a table with a tuple column that is made up of an int64 paired with a uuid:
CREATE TABLE ks.mytable {
fileid frozen <tuple <bigint, uuid>>,
hits counter,
...
and I can currently set the field using a cql statement like:
UPDATE ks.mytable hits = hits + 1 WHERE fileid=(? ?);
and I pass in 2 variables as arguments, an int64 and a gocql.UUID.
Instead of moving 2 variables around everywhere, I want to put these in a struct, something like
type MyID struct {
id int64
uid gocql.UUID
}
then use a Marshaller to pass these into the UPDATE statement.
Is this possible? I am not sure if I can pass in a single variable for the tuple field. If so, how can I do this? I can't figure out how - I was trying to mimic https://github.com/gocql/gocql/blob/master/marshal_test.go#L935 but I'm getting errors where I can't set the fields in the struct (cannot refer to unexported field or method proto)
As you mentioned, you are getting the following error:
cannot refer to unexported field or method proto
This means you need to export your fields inside the struct and that means beginning with a capital letter in Go. So your struct should be:
type MyID struct {
Id int64
Uid gocql.UUID
}
Then, it should work.
Related
I just started learning Golang today. So, I suppose this question is a basic one howerver I tried what I can try, but get error.
So, I have defined a Student struct type:
type Student struct {
firstname string `json:"first_name"`
id int `json:"id"`
}
I want to have a map data structure, in which the map's key represent "class id" & the value of each key in this map is an array of Student. This is what I have tried:
var studentsMap = make(map[int][]Student)
func registerStudent(classId int, studentName string, studentId int) {
var studentsInClass = studentsMap[classId]
if studentsInClass == nil {
studentsInClass = []Student{}
}
// append the new student to the studentsInClass array
var updatedStudentsArr = append(studentsInClass, Student{studentName, studentId})
// update the map for this class id with updated array of students
// Compiler ERROR: Cannot use 'updatedStudentsArr' (type []Student) as the type Student
studentsMap[classId] = updatedStudentsArr
}
As you see in my comment in the code, when I try to update the studentsMap with the new array, I get compiler error Cannot use 'updatedStudentsArr' (type []Student) as the type Student. Why is that? My guess is that I defined wrongly the studentsMap map type, but how to fix?
The code you posted seems to be working fine, as pointed out by #nipuna in the comments.
As a small note, when you test for a key,value existence in go you get two values, the latter being a boolean. You can thus use the following to test whether studentsMap[classId] exists
studentsInClass, ok := studentsMap[classId]
if !ok {
studentsInClass = []Student{}
}
Regarding your second question related to #Volker's comment, you can read more about exporting struct fields in the following answers.
If you are using an IDE, it might be warning you about it (e.g. in VSCode I get struct field firstname has json tag but is not exported).
https://stackoverflow.com/a/50320595/5621318
https://stackoverflow.com/a/11129474/5621318
https://stackoverflow.com/a/25595269/5621318
I have mentioned two fields(Name, Age) in my golang Struct after few days I have added one more fields in my database(Name,Age, Salary ) not in golandg struct.It shows errors like(Error 1364: Field 'salary' doesn't have a default value). How to ignore fileds in my struct dynamically
type Employee struct {
Name string `json:"name"
Age int `json:"age"
}
In future i will add more fileds but i don't want mention in struct
Based on the error you are getting, it seems like you are trying to insert a row into a MySQL database, and the new row you added does not have a default value. So your options are to :
Add a default value to the new column - See: https://dev.mysql.com/doc/refman/8.0/en/data-type-defaults.html
Add a field for the column into your Go struct and supply a value for it.
I'm using Go to create a nested struct and populate it. I have a custom field in the struct that I need to set myself, but it's a type used in a field of the outer struct. For example:
type Case struct {
CaseID string `json:"caseID"`
CaseStatus string `json:"caseStatus"`
Kit_Details []Kit_Details `json:"kit_Details"`
}
type Kit_Details struct {
KitID string `json:"kitID"`
KitStatus string `json:"kitStatus"`
}
I have created a nested struct. I want to update KitStatus fields using Case struct in my program.Means if I access Case struct from that how can i move to Kit_Details struct and update the field of a structure.
Can somebody help me how to loop through the fields of Case struct using FieldByName("KitStatus") and using SetString("New value") to update the value of that field.
You can use like this:
v := reflect.ValueOf(test)
fmt.Println("Value of test before update", v)
v.FieldByName("Kit_Details").Index(0).FieldByName("KitStatus").SetString("abcdsdf")
You can use a loop to traverse all the elements and update them using Index().
Go play ground link
From the documentation:
When query with struct, GORM will only query with those fields has non-zero value, that means if your field’s value is 0, '', false or other zero values, it won’t be used to build query conditions.
Here is an example of what I am trying to do :
type Dog struct {
ID uuid.UUID
OwnerID *uuid.UUID
}
The owner ID pointer may be nil.
db.Where("owner_id", nil).Find(&dogs)
But that returns all dogs (I expected this from the doc). I tried doing:
db.Where("owner_id", "NULL").Find(&dogs)
But that returns an empty list.
Is there a way to explicitly search for a NULL value field?
According to the docs, this should work:
db.Where("owner_id IS NULL").Find(&dogs)
Yeah, if you want to get the data with the value is null. You only have some choices.
use map interface
use struct with conditions
db.Where("owner_id IS NULL").Find(&dogs)
// or you can also try different way of writing
db.Find(&dogs, "owner_id IS NULL")
You were close in your original attempt. You can also achieve your desired result by writing the query as below.
db.Where("owner_id = ?", "NULL").Find(&dogs)
I have a model like this:
type Course struct {
Name string `db:"course_name"`
}
type Group struct {
Course *Course
}
type Groups []Group
And when i try to do sqlx.Select for Groups with a query like this:
SELECT c.name as course_name FROM courses as c;
I get
missing destination name course_name in *main.Groups
error.
What is the issue with this code?
You need to use sqlx.Select when you are selecting multiple rows and you want to scan the result into a slice, as is the case for your query, otherwise use sqlx.Get for a single row.
In addition, you can't scan directly into a Group struct because none of its fields are tagged (unlike the Course struct), and the Course field isn't embedded.
Try:
course := Course{}
courses := []Course{}
db.Get(&course, "SELECT name AS course_name FROM courses LIMIT 1")
db.Select(&courses, "SELECT name AS course_name FROM courses")
I changed Course *Course to Course Course - no effect.
When i made it embedded like this:
type Group struct {
Course
}
it worked.
This is also valid:
type Group struct {
*Course
}
Looks like sqlx doesn't understand anything except embedded fields.
Ok, so when you are using an embbeded struct with Sqlx, capitalization is important, at least in my case.
You need to refer to the embedded struct in your sql, like so:
select name as "course.name" from courses...
Notice that course is lower case and the naming involves a dot/period between table and column.
Then your Get or Select should work just fine.