Lyh data store

vendor/abcdb/storage/data_store.go

@@ -3,6 +3,7 @@ package storage
 import (
 	"abcdb/pager"
 	"abcdb/sql"
+	"errors"
 )
 
 // DataStore provids high level interfaces for retrieving and manipulating
@@ -11,12 +12,12 @@ import (
 // It only modifies data INDIRECTLY through Pager(see `pager.Pager`).
 type DataStore interface {
 	// LinearScan returns a `Stream` (see `storage.Stream`) that retrieves
-	// sql.Record lazily. `fields` determine the wanted field(s)
+	// sql.Record lazily. `targetfields` determine the wanted field(s)
 	//
 	// **contract**
 	//
-	// - `∀ field ∈ fields. field ∈ table.Fields`
-	LinearScan(table *sql.Table, fields []sql.Field) (RecordStream, error)
+	// - `∀ field ∈ targetfields. field ∈ table.Fields`
+	LinearScan(table *sql.Table, targetfields []sql.Field) (RecordStream, error)
 
 	// Insert returns nil or an error when
 	//
@@ -40,9 +41,93 @@ type RecordStream interface {
 	Next() (sql.Record, error)
 }
 
+// RecordLength : return the byte length of a record
+func RecordLength(table *sql.Table) int {
+	length := 0
+	for _, field := range table.Fields {
+		switch datatype := field.Type; datatype {
+		case sql.BOOL:
+			length++
+		case sql.INT32:
+			length += 4
+		case sql.DOUBLE:
+			length += 8
+		case sql.CHAR64:
+			length += 64
+		}
+	}
+	return length
+}
+
+type SimpleStream struct {
+	RecordList []sql.Record
+}
+
+func (SimpleStream *SimpleStream) Next() (sql.Record, error) {
+	if len(SimpleStream.RecordList) == 0 {
+		return nil, errors.New(
+			"no records left")
+	}
+	nextrecord := SimpleStream.RecordList[0]
+	SimpleStream.RecordList = SimpleStream.RecordList[1:]
+	return nextrecord, nil
+}
+
 // InitDataStore : initialize a `DataStore` instance with a `Pager` instance
 //   (see 'abcdb/pager/interface.go')
 func InitDataStore(pager pager.Pager) DataStore {
-	// TODO
+	return &SimpleManager{CurrentPager: pager}
+}
+
+type SimpleManager struct {
+	CurrentPager pager.Pager
+}
+
+func (SimpleManager *SimpleManager) LinearScan(
+	table *sql.Table, targetfields []sql.Field) (RecordStream, error) {
+	SimpleStream := &SimpleStream{RecordList: make([]sql.Record, 0)}
+	for i := 0; i <= table.NRecords; i++ {
+		byterecord := SimpleManager.CurrentPager.Read(
+			table.Name+"_records",
+			RecordLength(table)*i,
+			RecordLength(table))
+		record, err := MakeDeserializer(table).Deserialize(byterecord)
+		if err != nil {
+			return nil, err
+		}
+		targetrecord := make([]sql.Value, 0)
+		for _, targetfield := range targetfields {
+			for i, field := range table.Fields {
+				if targetfield == field {
+					targetrecord = append(targetrecord, record[i])
+				}
+			}
+		}
+		SimpleStream.RecordList = append(
+			SimpleStream.RecordList, targetrecord)
+	}
+	return SimpleStream, nil
+}
+
+func (SimpleManager *SimpleManager) Insert(
+	into *sql.Table, values []sql.FieldData) error {
+	orderedrecord := make([]sql.Value, 0)
+	for _, value := range values {
+		for _, field := range into.Fields {
+			if *value.Field == field {
+				orderedrecord = append(orderedrecord, value.Value)
+			}
+		}
+	}
+	SimpleManager.CurrentPager.Write(
+		into.Name+"_records",
+		into.NRecords*RecordLength(into), Serialize(orderedrecord))
+	return nil
+}
+
+func (SimpleManager *SimpleManager) Flush(tables []*sql.Table) error {
+	for _, table := range tables {
+		SimpleManager.CurrentPager.Flush(table.Name)
+	}
 	return nil
 }