I am in the process of developing a web API using Go and there is a lot of redundant database query scan code.
func (m *ContractModel) WorkQuestions(cid int) ([]models.WorkQuestion, error) {
results, err := m.DB.Query(queries.WORK_QUESTIONS, cid)
if err != nil {
return nil, err
}
var workQuestions []models.WorkQuestion
for results.Next() {
var wq models.WorkQuestion
err = results.Scan(&wq.ContractStateID, &wq.QuestionID, &wq.Question, &wq.ID, &wq.Answer, &wq.Compulsory)
if err != nil {
return nil, err
}
workQuestions = append(workQuestions, wq)
}
return workQuestions, nil
}
func (m *ContractModel) Questions(cid int) ([]models.Question, error) {
results, err := m.DB.Query(queries.QUESTIONS, cid)
if err != nil {
return nil, err
}
var questions []models.Question
for results.Next() {
var q models.Question
err = results.Scan(&q.Question, &q.Answer)
if err != nil {
return nil, err
}
questions = append(questions, q)
}
return questions, nil
}
func (m *ContractModel) Documents(cid int) ([]models.Document, error) {
results, err := m.DB.Query(queries.DOCUMENTS, cid)
if err != nil {
return nil, err
}
var documents []models.Document
for results.Next() {
var d models.Document
err = results.Scan(&d.Document, &d.S3Region, &d.S3Bucket, &d.Source)
if err != nil {
return nil, err
}
documents = append(documents, d)
}
return documents, nil
}
I need to generalize this code so that I can pass in the result *sql.Rows
to a function and obtain a struct slice containing the scanned rows. I know that there is a StructScan
method in sqlx package but this cannot be used since I have a significant amount of code written using the go standard database/sql package.
Using the reflect package, I can create a generic StructScan function but reflect package cannot create a slice of struct from a passed interface{} type. What I need to achieve is something like as follows
func RowsToStructs(rows *sql.Rows, model interface{}) ([]interface{}, error) {
// 1. Create a slice of structs from the passed struct type of model
// 2. Loop through each row,
// 3. Create a struct of passed mode interface{} type
// 4. Scan the row results to a slice of interface{}
// 5. Set the field values of struct created in step 3 using the slice in step 4
// 6. Add the struct created in step 3 to slice created in step 1
// 7. Return the struct slice
}
I cannot seem to find a way to scan the struct passed as the model parameter and create a slice of it using the reflect package. Is there any workaround to this or am I looking at the question in a wrong way?
Struct fields has the correct number of cols returned from the result and in correct order
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