Scan provides the ability to to scan sql rows directly to any defined structure.
MIT License
Scan provides the ability to use database/sql/rows to scan datasets directly to any defined structure.
database/sql
. Link
github.com/jackc/pgx/v5
. Link
scan.Queryer
. Link
database/sql
package main
import (
"context"
"database/sql"
"github.com/stephenafamo/scan"
"github.com/stephenafamo/scan/stdscan"
)
type User struct {
ID int
Name string
Email string
Age int
}
func main() {
ctx := context.Background()
db, _ := sql.Open("postgres", "example-connection-url")
// count: 5
count, _ := stdscan.One(ctx, db, scan.SingleColumnMapper[int], "SELECT COUNT(*) FROM users")
// []int{1, 2, 3, 4, 5}
userIDs, _ := stdscan.All(ctx, db, scan.SingleColumnMapper[int], "SELECT id FROM users")
// []User{...}
users, _ := stdscan.All(ctx, db, scan.StructMapper[User](), `SELECT id, name, email, age FROM users`)
}
func collectIDandEmail(_ context.Context, c cols) any {
return func(v *Values) (int, string, error) {
return Value[int](v, "id"), Value[string](v, "email"), nil
}
}
And many more!!
ctx := context.Background()
db, _ := pgxpool.New(ctx, "example-connection-url")
// []User{...}
users, _ := pgxscan.All(ctx, db, scan.StructMapper[User](), `SELECT id, name, email, age FROM users`)
Instead of github.com/stephenafamo/scan/stdscan
, use the base package github.com/stephenafam/scan
which only needs an executor that implements the right interface.
Both stdscan
and pgxscan
are based on this.
One()
Use One()
to scan and return a single row.
// User{...}
user, _ := stdscan.One(ctx, db, scan.StructMapper[User](), `SELECT id, name, email, age FROM users`)
All()
Use All()
to scan and return all rows.
// []User{...}
users, _ := stdscan.All(ctx, db, scan.StructMapper[User](), `SELECT id, name, email, age FROM users`)
Each()
Use Each()
to iterate over the rows of a query using range.
It works with the range-over-func syntax.
// []User{...}
users, _ := stdscan.All(ctx, db, scan.StructMapper[User](), `SELECT id, name, email, age FROM users`)
for user, err := range scan.Each(ctx, db, scan.StructMapper[User](), `SELECT id, name, email, age FROM users`) {
if err != nil {
return err
}
// do something with user
}
Cursor()
Use Cursor()
to scan each row on demand. This is useful when retrieving large results.
c, _ := stdscan.Cursor(ctx, db, scan.StructMapper[User](), `SELECT id, name, email, age FROM users`)
defer c.Close()
for c.Next() {
// User{...}
user := c.Get()
}
Each of these functions takes a Mapper
to indicate how each row should be scanned.
The Mapper
has the signature:
type Mapper[T any] func(context.Context, cols) (before BeforeFunc, after func(any) (T, error))
type BeforeFunc = func(*Row) (link any, err error)
A mapper returns 2 functions
ScheduleScan
or ScheduleScanx
methods of the Row
. The return value of the before function is passed to the after function after scanning values from the database.There are some builtin mappers for common cases:
ColumnMapper[T any](name string)
Maps the value of a single column to the given type. The name of the column must be specified
// []string{"[email protected]", "[email protected]", "[email protected]", ...}
emails, _ := stdscan.All(ctx, db, scan.ColumnMapper[string]("email"), `SELECT id, name, email FROM users`)
SingleColumnMapper[T any]
For queries that return only one column. Since only one column is returned, there is no need to specify the column name. This is why it throws an error if the query returns more than one column.
// []string{"[email protected]", "[email protected]", "[email protected]", ...}
emails, _ := stdscan.All(ctx, db, scan.SingleColumnMapper[string], `SELECT email FROM users`)
SliceMapper[T any]
Maps a row into a slice of values []T
. Unless all the columns are of the same type, it will likely be used to map the row to []any
.
// [][]any{
// []any{1, "John Doe", "[email protected]"},
// []any{2, "Jane Doe", "[email protected]"},
// ...
// }
users, _ := stdscan.All(ctx, db, scan.SliceMapper[any], `SELECT id, name, email FROM users`)
MapMapper[T any]
Maps a row into a map of values map[string]T
. The key of the map is the column names. Unless all columns are of the same type, it will likely be used to map to map[string]any
.
// []map[string]any{
// map[string]any{"id": 1, "name": John Doe", "email": "[email protected]"},
// map[string]any{"id": 2, "name": Jane Doe", "email": "[email protected]"},
// ...
// }
users, _ := stdscan.All(ctx, db, scan.MapMapper[any], `SELECT id, name, email FROM users`)
StructMapper[T any](...MappingOption)
This is the most advanced mapper. Scans column values into the fields of the struct.
type User struct {
ID int `db:"id"`
Name string `db:"name"`
Email string `db:"email"`
Age int `db:"age"`
}
// []User{...}
users, _ := stdscan.All(ctx, db, scan.StructMapper[User](), `SELECT id, name, email, age FROM users`)
The default behaviour of StructMapper
is often good enough. For more advanced use cases, some options can be passed to the StructMapper.
WithStructTagPrefix: Use this when every column from the database has a prefix.
users, _ := stdscan.All(ctx, db, scan.StructMapper[User](scan.WithStructTagPrefix("user-")),
`SELECT id AS "user-id", name AS "user-name" FROM users`,
)
WithRowValidator: If the StructMapper
has a row validator, the values will be sent to it before scanning. If the row is invalid (i.e. it returns false), then scanning is skipped and the zero value of the row-type is returned.
WithTypeConverter: If the StructMapper
has a type converter, all fields of the struct are converted to a new type using the ConverType
method. After scanning, the values are restored into the struct using the OriginalValue
method.
CustomStructMapper[T any](MapperSource, ...MappingSourceOption)
Uses a custom struct maping source which should have been created with NewStructMapperSource.
This works the same way as StructMapper
, but instead of using the default mapping source, it uses a custom one.
In the example below, we want to use a scan
as the struct tag key instead of db
type User struct {
ID int `scan:"id"`
Name string `scan:"name"`
Email string `scan:"email"`
Age int `scan:"age"`
}
src, _ := NewStructMapperSource(scan.WithStructTagKey("scan"))
// []User{...}
users, _ := stdscan.All(ctx, db, scan.StructMapper[User](), `SELECT id, name, email, age FROM users`)
These are the options that can be passed to NewStructMapperSource
:
CreatedAt
is mapped to created_at
).*sql.Scanner
.