qb: update builder advanced assignments

qb/update.go

@@ -9,16 +9,41 @@ package qb
 
 import (
 	"bytes"
+	"fmt"
 )
 
+// assignment specifies an assignment in a set operation.
+type assignment struct {
+	column string
+	name   string
+	expr   bool
+	fn     *Func
+}
+
+func (a assignment) writeCql(cql *bytes.Buffer) (names []string) {
+	cql.WriteString(a.column)
+	switch {
+	case a.expr:
+		names = append(names, a.name)
+	case a.fn != nil:
+		cql.WriteByte('=')
+		names = append(names, a.fn.writeCql(cql)...)
+	default:
+		cql.WriteByte('=')
+		cql.WriteByte('?')
+		names = append(names, a.name)
+	}
+	return
+}
+
 // UpdateBuilder builds CQL UPDATE statements.
 type UpdateBuilder struct {
-	table   string
-	using   using
-	columns columns
-	where   where
-	_if     _if
-	exists  bool
+	table       string
+	using       using
+	assignments []assignment
+	where       where
+	_if         _if
+	exists      bool
 }
 
 // Update returns a new UpdateBuilder with the given table name.
@@ -39,14 +64,12 @@ func (b *UpdateBuilder) ToCql() (stmt string, names []string) {
 	names = append(names, b.using.writeCql(&cql)...)
 
 	cql.WriteString("SET ")
-	for i, c := range b.columns {
-		cql.WriteString(c)
-		cql.WriteString("=?")
-		if i < len(b.columns)-1 {
+	for i, a := range b.assignments {
+		names = append(names, a.writeCql(&cql)...)
+		if i < len(b.assignments)-1 {
 			cql.WriteByte(',')
 		}
 	}
-	names = append(names, b.columns...)
 	cql.WriteByte(' ')
 
 	names = append(names, b.where.writeCql(&cql)...)
@@ -80,7 +103,51 @@ func (b *UpdateBuilder) TTL() *UpdateBuilder {
 
 // Set adds SET clauses to the query.
 func (b *UpdateBuilder) Set(columns ...string) *UpdateBuilder {
-	b.columns = append(b.columns, columns...)
+	for _, c := range columns {
+		b.assignments = append(b.assignments, assignment{
+			column: c,
+			name:   c,
+		})
+	}
+
+	return b
+}
+
+// SetFunc adds SET column=someFunc(?...) clause to the query.
+func (b *UpdateBuilder) SetFunc(column string, fn *Func) *UpdateBuilder {
+	b.assignments = append(b.assignments, assignment{column: column, fn: fn})
+	return b
+}
+
+// Add adds SET column=column+? clauses to the query.
+func (b *UpdateBuilder) Add(column string) *UpdateBuilder {
+	return b.AddNamed(column, column)
+}
+
+// AddNamed adds SET column=column+? clauses to the query with a custom
+// parameter name.
+func (b *UpdateBuilder) AddNamed(column, name string) *UpdateBuilder {
+	b.assignments = append(b.assignments, assignment{
+		column: fmt.Sprint(column, "=", column, "+?"),
+		name:   name,
+		expr:   true,
+	})
+	return b
+}
+
+// Remove adds SET column=column-? clauses to the query.
+func (b *UpdateBuilder) Remove(column string) *UpdateBuilder {
+	return b.RemoveNamed(column, column)
+}
+
+// RemoveNamed adds SET column=column-? clauses to the query with a custom
+// parameter name.
+func (b *UpdateBuilder) RemoveNamed(column, name string) *UpdateBuilder {
+	b.assignments = append(b.assignments, assignment{
+		column: fmt.Sprint(column, "=", column, "-?"),
+		name:   name,
+		expr:   true,
+	})
 	return b
 }