Introduce QueryBuilder type

database/query_builder.go

@@ -0,0 +1,254 @@
+package database
+
+import (
+	"fmt"
+	"golang.org/x/exp/slices"
+	"reflect"
+	"sort"
+	"strings"
+)
+
+// QueryBuilder is an addon for the [DB] type that takes care of all the database statement building shenanigans.
+// The recommended use of QueryBuilder is to only use it to generate a single query at a time and not two different
+// ones. If for instance you want to generate `INSERT` and `SELECT` queries, it is best to use two different
+// QueryBuilder instances. You can use the DB#QueryBuilder() method to get fully initialised instances each time.
+type QueryBuilder struct {
+	db *DB
+
+	subject         any
+	columns         []string
+	excludedColumns []string
+
+	// Indicates whether the generated columns should be sorted in ascending order before generating the
+	// actual statements. This is intended for unit tests only and shouldn't be necessary for production code.
+	sort bool
+}
+
+// SetColumns sets the DB columns to be used when building the statements.
+// When you do not want the columns to be extracted dynamically, you can use this method to specify them manually.
+// Returns the current *[QueryBuilder] receiver and allows you to chain some method calls.
+func (qb *QueryBuilder) SetColumns(columns ...string) *QueryBuilder {
+	qb.columns = columns
+	return qb
+}
+
+// SetExcludedColumns excludes the given columns from all the database statements.
+// Returns the current *[QueryBuilder] receiver and allows you to chain some method calls.
+func (qb *QueryBuilder) SetExcludedColumns(columns ...string) *QueryBuilder {
+	qb.excludedColumns = columns
+	return qb
+}
+
+// Delete returns a DELETE statement for the query builders subject filtered by ID.
+func (qb *QueryBuilder) Delete() string {
+	return qb.DeleteBy("id")
+}
+
+// DeleteBy returns a DELETE statement for the query builders subject filtered by the given column.
+func (qb *QueryBuilder) DeleteBy(column string) string {
+	return fmt.Sprintf(`DELETE FROM "%s" WHERE "%s" IN (?)`, TableName(qb.subject), column)
+}
+
+// Insert returns an INSERT INTO statement for the query builders subject.
+func (qb *QueryBuilder) Insert() (string, int) {
+	columns := qb.BuildColumns()
+
+	return fmt.Sprintf(
+		`INSERT INTO "%s" ("%s") VALUES (%s)`,
+		TableName(qb.subject),
+		strings.Join(columns, `", "`),
+		fmt.Sprintf(":%s", strings.Join(columns, ", :")),
+	), len(columns)
+}
+
+// InsertIgnore returns an INSERT statement for the query builders subject for
+// which the database ignores rows that have already been inserted.
+func (qb *QueryBuilder) InsertIgnore() (string, int) {
+	columns := qb.BuildColumns()
+
+	var clause string
+	switch qb.db.DriverName() {
+	case MySQL:
+		// MySQL treats UPDATE id = id as a no-op.
+		clause = fmt.Sprintf(`ON DUPLICATE KEY UPDATE "%[1]s" = "%[1]s"`, columns[0])
+	case PostgreSQL:
+		clause = fmt.Sprintf("ON CONFLICT ON CONSTRAINT %s DO NOTHING", qb.getPgsqlOnConflictConstraint())
+	default:
+		panic("Driver unsupported: " + qb.db.DriverName())
+	}
+
+	return fmt.Sprintf(
+		`INSERT INTO "%s" ("%s") VALUES (%s) %s`,
+		TableName(qb.subject),
+		strings.Join(columns, `", "`),
+		fmt.Sprintf(":%s", strings.Join(columns, ", :")),
+		clause,
+	), len(columns)
+}
+
+// Select returns a SELECT statement from the query builders subject and the already set columns.
+// If no columns are set, they will be extracted from the query builders subject.
+// When the query builders subject is of type Scoper, a WHERE clause is appended to the statement.
+func (qb *QueryBuilder) Select() string {
+	var scoper Scoper
+	if sc, ok := qb.subject.(Scoper); ok {
+		scoper = sc
+	}
+
+	return qb.SelectScoped(scoper)
+}
+
+// SelectScoped returns a SELECT statement from the query builders subject and the already set columns filtered
+// by the given scoper/column. When no columns are set, they will be extracted from the query builders subject.
+// The argument scoper must either be of type Scoper, string or nil to get SELECT statements without a WHERE clause.
+func (qb *QueryBuilder) SelectScoped(scoper any) string {
+	query := fmt.Sprintf(`SELECT "%s" FROM "%s"`, strings.Join(qb.BuildColumns(), `", "`), TableName(qb.subject))
+	where, placeholders := qb.Where(scoper)
+	if placeholders > 0 {
+		query += ` WHERE ` + where
+	}
+
+	return query
+}
+
+// Update returns an UPDATE statement for the query builders subject filter by ID column.
+func (qb *QueryBuilder) Update() (string, int) {
+	return qb.UpdateScoped("id")
+}
+
+// UpdateScoped returns an UPDATE statement for the query builders subject filtered by the given column/scoper.
+// The argument scoper must either be of type Scoper, string or nil to get UPDATE statements without a WHERE clause.
+func (qb *QueryBuilder) UpdateScoped(scoper any) (string, int) {
+	columns := qb.BuildColumns()
+	set := make([]string, 0, len(columns))
+
+	for _, col := range columns {
+		set = append(set, fmt.Sprintf(`"%[1]s" = :%[1]s`, col))
+	}
+
+	placeholders := len(columns)
+	query := `UPDATE "%s" SET %s`
+	if where, count := qb.Where(scoper); count > 0 {
+		placeholders += count
+		query += ` WHERE ` + where
+	}
+
+	return fmt.Sprintf(query, TableName(qb.subject), strings.Join(set, ", ")), placeholders
+}
+
+// Upsert returns an upsert statement for the query builders subject.
+func (qb *QueryBuilder) Upsert() (string, int) {
+	var updateColumns []string
+	if upserter, ok := qb.subject.(Upserter); ok {
+		updateColumns = qb.db.columnMap.Columns(upserter.Upsert())
+	} else {
+		updateColumns = qb.BuildColumns()
+	}
+
+	return qb.UpsertColumns(updateColumns...)
+}
+
+// UpsertColumns returns an upsert statement for the query builders subject and the specified update columns.
+func (qb *QueryBuilder) UpsertColumns(updateColumns ...string) (string, int) {
+	var clause, setFormat string
+	switch qb.db.DriverName() {
+	case MySQL:
+		clause = "ON DUPLICATE KEY UPDATE"
+		setFormat = `"%[1]s" = VALUES("%[1]s")`
+	case PostgreSQL:
+		clause = fmt.Sprintf("ON CONFLICT ON CONSTRAINT %s DO UPDATE SET", qb.getPgsqlOnConflictConstraint())
+		setFormat = `"%[1]s" = EXCLUDED."%[1]s"`
+	default:
+		panic("Driver unsupported: " + qb.db.DriverName())
+	}
+
+	set := make([]string, 0, len(updateColumns))
+	for _, col := range updateColumns {
+		set = append(set, fmt.Sprintf(setFormat, col))
+	}
+
+	insertColumns := qb.BuildColumns()
+
+	return fmt.Sprintf(
+		`INSERT INTO "%s" ("%s") VALUES (%s) %s %s`,
+		TableName(qb.subject),
+		strings.Join(insertColumns, `", "`),
+		fmt.Sprintf(":%s", strings.Join(insertColumns, ", :")),
+		clause,
+		strings.Join(set, ", "),
+	), len(insertColumns)
+}
+
+// Where returns a WHERE clause with named placeholder conditions built from the
+// specified scoper/column combined with the AND operator.
+func (qb *QueryBuilder) Where(subject any) (string, int) {
+	t := reflect.TypeOf(subject)
+	if t == nil { // Subject is a nil interface value.
+		return "", 0
+	}
+
+	var columns []string
+	if t.Kind() == reflect.String {
+		columns = []string{subject.(string)}
+	} else if t.Kind() == reflect.Struct || t.Kind() == reflect.Pointer {
+		if scoper, ok := subject.(Scoper); ok {
+			return qb.Where(scoper.Scope())
+		}
+
+		columns = qb.db.columnMap.Columns(subject)
+	} else { // This should never happen unless someone wants to do some silly things.
+		panic(fmt.Sprintf("qb.Where: unknown subject type provided: %q", t.Kind().String()))
+	}
+
+	where := make([]string, 0, len(columns))
+	for _, col := range columns {
+		where = append(where, fmt.Sprintf(`"%[1]s" = :%[1]s`, col))
+	}
+
+	return strings.Join(where, ` AND `), len(columns)
+}
+
+// BuildColumns returns all the Query Builder columns (if specified), otherwise they are
+// determined dynamically using its subject. Additionally, it checks whether columns need
+// to be excluded and proceeds accordingly.
+func (qb *QueryBuilder) BuildColumns() []string {
+	var columns []string
+	if len(qb.columns) > 0 {
+		columns = qb.columns
+	} else {
+		columns = qb.db.columnMap.Columns(qb.subject)
+	}
+
+	if len(qb.excludedColumns) > 0 {
+		columns = slices.DeleteFunc(append([]string(nil), columns...), func(column string) bool {
+			for _, exclude := range qb.excludedColumns {
+				if exclude == column {
+					return true
+				}
+			}
+
+			return false
+		})
+	}
+
+	if qb.sort {
+		// The order in which the columns appear is not guaranteed as we extract the columns dynamically
+		// from the struct. So, we've to sort them here to be able to test the generated statements.
+		sort.SliceStable(columns, func(a, b int) bool {
+			return columns[a] < columns[b]
+		})
+	}
+
+	return columns
+}
+
+// getPgsqlOnConflictConstraint returns the constraint name of the current [QueryBuilder]'s subject.
+// If the subject does not implement the PgsqlOnConflictConstrainter interface, it will simply return
+// the table name prefixed with `pk_`.
+func (qb *QueryBuilder) getPgsqlOnConflictConstraint() string {
+	if constrainter, ok := qb.subject.(PgsqlOnConflictConstrainter); ok {
+		return constrainter.PgsqlOnConflictConstraint()
+	}
+
+	return "pk_" + TableName(qb.subject)
+}