Add simple support for locking reads, FOR UPDATE clause

query_builder.go

@@ -29,6 +29,8 @@ type QueryBuilder interface {
  BuildOrderByAndLimit(string, []string, int64, int64) string
  // BuildUnion generates a UNION clause from the given union information.
  BuildUnion([]UnionInfo, Params) string
+ // BuildFor generates a FOR UPDATE clause from the given expression
+ BuildFor(option string) string
 }
 
 // BaseQueryBuilder provides a basic implementation of QueryBuilder.
@@ -234,6 +236,16 @@ func (q *BaseQueryBuilder) BuildLimit(limit int64, offset int64) string {
  return sql + fmt.Sprintf("OFFSET %v", offset)
 }
 
+func (q *BaseQueryBuilder) BuildFor(option string) string {
+ s := ""
+ if option != "" {
+ s += option
+ } else {
+ s += "UPDATE "
+ }
+ return "FOR " + s
+}
+
 func (q *BaseQueryBuilder) quoteTableNameAndAlias(table string) string {
  matches := selectRegex.FindStringSubmatch(table)
  if len(matches) == 0 {

select.go

@@ -21,19 +21,20 @@ type SelectQuery struct {
  builder Builder
  ctx context.Context
 
- selects []string
- distinct bool
- selectOption string
- from []string
- where Expression
- join []JoinInfo
- orderBy []string
- groupBy []string
- having Expression
- union []UnionInfo
- limit int64
- offset int64
- params Params
+ selects []string
+ distinct bool
+ selectOption string
+ from []string
+ where Expression
+ join []JoinInfo
+ orderBy []string
+ groupBy []string
+ having Expression
+ union []UnionInfo
+ limit int64
+ offset int64
+ params Params
+ lockingOption string
 }
 
 // JoinInfo contains the specification for a JOIN clause.
@@ -68,14 +69,14 @@ func NewSelectQuery(builder Builder, db *DB) *SelectQuery {
 }
 
 // Context returns the context associated with the query.
-func (q *SelectQuery) Context() context.Context {
- return q.ctx
+func (s *SelectQuery) Context() context.Context {
+ return s.ctx
 }
 
 // WithContext associates a context with the query.
-func (q *SelectQuery) WithContext(ctx context.Context) *SelectQuery {
- q.ctx = ctx
- return q
+func (s *SelectQuery) WithContext(ctx context.Context) *SelectQuery {
+ s.ctx = ctx
+ return s
 }
 
 // Select specifies the columns to be selected.
@@ -245,6 +246,12 @@ func (s *SelectQuery) AndBind(params Params) *SelectQuery {
  return s
 }
 
+// For appends the FOR UPDATE or FOR SHARING clause
+func (s *SelectQuery) For(option string) *SelectQuery {
+ s.lockingOption = option
+ return s
+}
+
 // Build builds the SELECT query and returns an executable Query object.
 func (s *SelectQuery) Build() *Query {
  params := Params{}
@@ -261,6 +268,7 @@ func (s *SelectQuery) Build() *Query {
  qb.BuildWhere(s.where, params),
  qb.BuildGroupBy(s.groupBy),
  qb.BuildHaving(s.having, params),
+ qb.BuildFor(s.lockingOption),
  }
  sql := ""
  for _, clause := range clauses {