csvq driver
A go database/sql driver for csvq.
csvq-driver allows you to operate csv files and other supported formats using csvq statements in Go. You can use the statements in the same way as other relational database systems.
Requirements
Go 1.12 or later (ref. Getting Started - The Go Programming Language)
Supported features
- Query
- Only the result-sets in the top-level scope can be retrieved. You cannot refer the results of child scopes such as inside of IF, WHILE and user-defined functions.
- Exec
- Only the last result in the top-level scope can be retrieved.
- LastInsertId is not supported.
- Prepared Statement
- Ordinal placeholders
- Named placeholders
- Transaction
- Isolation Level is the default only.
- Read-only transaction is not supported.
- If you do not use the database/sql transaction feature, all execusions will commit at the end of the execusion automatically.
Usage
Data Source Name
A data source name to call sql.Open is a directory path. It is the same as "--repository" option of the csvq command.
Error Handling
If a received error is a returned error from csvq, you can cast the error to github.com/mithrandie/csvq/lib/query.Error interface. The error interface has following functions.
function | description |
---|---|
Message() string | Error message |
Code() int | Error code. The same as the exit code of the csvq command |
Number() int | Error number |
Line() int | Line number where the error occurred in the passed statement |
Char() int | Column number where the error occurred in the passed statement |
Source() string | File or statement name where the error occurred |
Example
package main
import (
"context"
"database/sql"
"fmt"
"github.com/mithrandie/csvq/lib/query"
_ "github.com/mithrandie/csvq-driver"
)
func main() {
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()
db, err := sql.Open("csvq", "/path/to/data/directory")
if err != nil {
panic(err)
}
defer func() {
if err := db.Close(); err != nil {
panic(err)
}
}()
queryString := "SELECT id, first_name, country_code FROM `users.csv` WHERE id = '12'"
r := db.QueryRowContext(ctx, queryString)
var (
id int
firstName string
countryCode string
)
if err := r.Scan(&id, &firstName, &countryCode); err != nil {
if err == sql.ErrNoRows {
fmt.Println("No Rows.")
} else if csvqerr, ok := err.(query.Error); ok {
panic(fmt.Sprintf("Unexpected error: Number: %d Message: %s", csvqerr.Number(), csvqerr.Message()))
} else {
panic("Unexpected error: " + err.Error())
}
} else {
fmt.Printf("Result: [id]%3d [first_name]%10s [country_code]%3s\n", id, firstName, countryCode)
}
}
See: https://github.com/mithrandie/csvq-driver/blob/master/example/csvq-driver/csvq-driver-example.go
Replace I/O
You can replace input/output interface of the csvq to pass the data from inside of your go programs or retrive the result-sets as a another format.
function in the csvq-driver | default | description |
---|---|---|
SetStdin(r io.ReadCloser) error SetStdinContext(ctx context.Context, r io.ReadCloser) error |
os.Stdin | Replace input interface. Passed data can be refered as a temporary table named "STDIN". |
SetStdout(w io.WriteCloser) | query.Discard | Replace output interface. Logs and result-sets of select queries are written to stdout. |
SetOutFile(w io.Writer) | nil | Put a writer for result-sets of select queries to write instead of stdout. |
The following structs are available for replacement.
struct name | initializer |
---|---|
query.Input | query.NewInput(r io.Reader) |
query.Output | query.NewOutput() |
"query" means the package "github.com/mithrandie/csvq/lib/query".
See: https://github.com/mithrandie/csvq-driver/blob/master/example/replace-io/csvq-replace-io-example.go