Using Bind() function in gocql
Vivek Bhat
Hi all,
Currently our service uses gocql to fetch the data from Apache Cassandra. In Cassandra the usage of query with `where in` is not recommended due to performance issues. So I was trying to implement the execution of the select query parallel to Cassandra using go routines.
Example:
A request for 5 gtin13s would create 5 different goroutines of `p.getAll` and would then run generate the result.
My question:
Currently I’m creating multiple instances of `gocql.Query` in the call for function `getAlll` because if I try to use the same instance of `gocql.Query` the bind would not work and result in duplicate values.
Is there an alternative approach of doing this? Please help me on this.
```
type dbRespWithErrors struct {
Gtin13 string
Product Product
Err error
}
type Product{
Gtin13 string
Name string
}
func (p product) GetProducts(session *gocql.Session, gtin13s []string) ([]Product, error) {
var productCounter = 0
respFromDB := make(chan dbRespWithErrors, len(gtin13s))
query := " Select " + columns + " from " + dto.Products
if len(gtin13s) > 0 {
query = query + " where Gtin13 = ?"
}
preparedQuery := session.Query(query)
for _, gtin13 := range gtin13s {
//Creating multiple instance of prepared query when we call the getAll function
go p.getAll(*preparedQuery, gtin13, respFromDB)
}
var prods []dto.Product
for p := range respFromDB {
productCounter++
if p.Product != nil {
prods = append(prods, *p.Product)
}
if productCounter == len(gtin13s) {
close(respFromDB)
}
}
return prods, nil
}
func (p product) getAll(preparedStatement gocql.Query, gtin13 string, product chan dbRespWithErrors) {
var (
err error
prodResp dbRespWithErrors
)
prod := Product{}
prodResp = dbRespWithErrors{
Gtin13: gtin13,
}
err = preparedStatement.Bind(gtin13).Scan(&prod.gtin13,&prod.Name)
if err != nil {
prodResp.Err = err
product <- prodResp
return
}
prodResp.Product = &prod
product <- prodResp
}
```
Also we had migrated the data from Apache Cassandra to cosmos db Cassandra API.
And when we tried running the same code above the output was quite unexpected.
For example:
A function call like
`p.GetProducts(session,[]string{“12345”,”12346”,“12347”,”12348”,“12349”})`
Would result in the response
```
[]Product{
{
Gtin13:12345
Name:x
},
{
Gtin13:12346
Name:y
},
{
Gtin13:12345
Name:x
},
{
Gtin13:12348
Name:z
},
{
Gtin13:12346
Name:y
}
}
```
I.e some of the rows are repeated and others are ignored. How can I debug this specific issue? Any help would be appreciated.
Thanks and regards,
Vivek Bhat
night...@googlemail.com
col2_value := 1
session.Query("SELECT col1 FROM my table WHERE col2=?;", col2_value)
is all that you need for safe, easy and peformant query execution. gocql automatically prepares the statements for you and caches prepared statements.