qb: select

qb/select.go

@@ -0,0 +1,153 @@
+package qb
+
+// SELECT reference:
+// http://docs.datastax.com/en/dse/5.1/cql/cql/cql_reference/cql_commands/cqlSelect.html
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+)
+
+type Order bool
+
+const (
+	ASC  Order = true
+	DESC       = false
+)
+
+type SelectBuilder struct {
+	table             string
+	columns           columns
+	distinct          columns
+	where             where
+	groupBy           columns
+	orderBy           string
+	order             Order
+	limit             uint
+	limitPerPartition uint
+	allowFiltering    bool
+}
+
+// Select returns a new SelectBuilder with the given table name.
+func Select(table string) *SelectBuilder {
+	return &SelectBuilder{
+		table: table,
+	}
+}
+
+func (b *SelectBuilder) ToCql() (stmt string, names []string, err error) {
+	if b.table == "" {
+		err = errors.New("select statements must specify a table")
+		return
+	}
+	if b.distinct != "" && len(b.columns) > 0 {
+		err = fmt.Errorf("select statements must specify either a column list or DISTINCT partition_key")
+		return
+	}
+
+	cql := bytes.Buffer{}
+
+	cql.WriteString("SELECT ")
+	switch {
+	case len(b.distinct) > 0:
+		cql.WriteString("DISTINCT ")
+		b.distinct.writeCql(&cql)
+	case len(b.groupBy) > 0:
+		b.groupBy.writeCql(&cql)
+		cql.WriteByte(',')
+		b.columns.writeCql(&cql)
+	case len(b.columns) == 0:
+		cql.WriteByte('*')
+	default:
+		b.columns.writeCql(&cql)
+	}
+	cql.WriteString(" FROM ")
+	cql.WriteString(b.table)
+	cql.WriteByte(' ')
+
+	names = b.where.writeCql(&cql)
+
+	if len(b.groupBy) > 0 {
+		cql.WriteString("GROUP BY ")
+		b.groupBy.writeCql(&cql)
+		cql.WriteByte(' ')
+	}
+
+	if b.orderBy != "" {
+		cql.WriteString("ORDER BY ")
+		cql.WriteString(b.orderBy)
+		if b.order {
+			cql.WriteString(" ASC ")
+		} else {
+			cql.WriteString(" DESC ")
+		}
+	}
+
+	if b.limit != 0 {
+		cql.WriteString("LIMIT ")
+		cql.WriteString(fmt.Sprint(b.limit))
+		cql.WriteByte(' ')
+	}
+
+	if b.limitPerPartition != 0 {
+		cql.WriteString("PER PARTITION LIMIT ")
+		cql.WriteString(fmt.Sprint(b.limitPerPartition))
+		cql.WriteByte(' ')
+	}
+
+	if b.allowFiltering {
+		cql.WriteString("ALLOW FILTERING ")
+	}
+
+	stmt = cql.String()
+	return
+}
+
+// From sets the table to be selected from.
+func (b *SelectBuilder) From(table string) *SelectBuilder {
+	b.table = table
+	return b
+}
+
+func (b *SelectBuilder) Columns(columns ...string) *SelectBuilder {
+	b.columns = append(b.columns, columns...)
+	return b
+}
+
+func (b *SelectBuilder) Distinct(columns... string) *SelectBuilder {
+	b.distinct = append(b.distinct, columns...)
+	return b
+}
+
+func (b *SelectBuilder) Where(e ...expr) *SelectBuilder {
+	b.where = append(b.where, e...)
+	return b
+}
+
+// GroupBy sets GROUP BY clause on the query. Columns must be a primary key,
+// this will automatically add the the columns as first selectors.
+func (b *SelectBuilder) GroupBy(columns... string) *SelectBuilder {
+	b.groupBy = append(b.groupBy, columns...)
+	return b
+}
+
+func (b *SelectBuilder) OrderBy(column string, o Order) *SelectBuilder {
+	b.orderBy, b.order = column, o
+	return b
+}
+
+func (b *SelectBuilder) Limit(limit uint) *SelectBuilder {
+	b.limit = limit
+	return b
+}
+
+func (b *SelectBuilder) LimitPerPartition(limit uint) *SelectBuilder {
+	b.limitPerPartition = limit
+	return b
+}
+
+func (b *SelectBuilder) AllowFiltering() *SelectBuilder {
+	b.allowFiltering = true
+	return b
+}