query.go

package kin

import (
	"fmt"
	_ "github.com/lib/pq" // Needed to initialize the Postgres SQL driver.
	"reflect"
	"strings"
)

// Query is an interface for generating query queries. It supports
// a few common and simple querying operations and then allows the user
// to solve more complex problems using SQL.
type Query[T Model] interface {
	// Get runs a select and returns all results.
	Get(table string) ([]*T, error)

	// Insert adds a record and returns the result.
	Insert(model T) (*T, error)

	// Raw generates a new statement to be executed at a later time.
	Raw(stmt string, params ...interface{}) *Statement[T]
}

// NewQuery creates a new wrapper around an existing DB connection.
func NewQuery[T Model](db DatabaseConnection) Query[T] {
	return &query[T]{db: db}
}

type query[T Model] struct {
	db DatabaseConnection
}

func (q *query[T]) Get(table string) ([]*T, error) {
	query := fmt.Sprintf("SELECT * FROM %s", table)
	return q.Raw(query).Many()
}

func (q *query[T]) Insert(model T) (*T, error) {
	return q.insertQuery(model).One()
}

func (q *query[T]) insertQuery(m Model) *Statement[T] {
	var columns string
	var values string
	var params []interface{}

	for _, details := range columnsWithValues(m) {
		if details.IsPrimaryKey {
			continue
		}

		separator := ""
		if len(params) > 0 {
			separator = ", "
		}

		params = append(params, details.Value)
		columns = fmt.Sprintf("%s%s%s", columns, separator, details.Name)
		values = fmt.Sprintf("%s%s$%d", values, separator, len(params))
	}

	stmt := fmt.Sprintf("INSERT INTO %s (%s) VALUES (%s) RETURNING *", m.TableName(), columns, values)

	return q.Raw(stmt, params...)
}

func (q *query[T]) Raw(stmt string, params ...interface{}) *Statement[T] {
	return &Statement[T]{
		db:     q.db,
		stmt:   stmt,
		params: params,
	}
}

type columnDetails struct {
	Name         string
	Value        interface{}
	IsPrimaryKey bool
}

func columnsWithValues[T Model](model T) []columnDetails {
	var details []columnDetails
	t := reflect.TypeOf(model)
	v := reflect.ValueOf(model)

	if t.Kind() == reflect.Ptr {
		t = t.Elem()
	}

	if v.Kind() == reflect.Ptr {
		v = v.Elem()
	}

	for i := 0; i < t.NumField(); i++ {
		field := t.Field(i)

		tags := field.Tag.Get("db")
		if tags == "" {
			continue
		}

		name := ""
		isPrimaryKey := false
		for _, tag := range strings.Split(tags, ",") {
			if tag == "primaryKey" {
				isPrimaryKey = true
			} else {
				name = tag
			}
		}

		details = append(details, columnDetails{
			Name:         name,
			Value:        v.Field(i).Interface(),
			IsPrimaryKey: isPrimaryKey,
		})
	}

	return details
}