feat: implement MSSQL data extraction and transformation process

cmd/go_migrate/extractor.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"context"
+	"database/sql"
+
+	_ "github.com/microsoft/go-mssqldb"
+	log "github.com/sirupsen/logrus"
+)
+
+type UnknownRowValues []any
+
+func extractFromMssql(ctx context.Context, job MigrationJob, columns []ColumnType, chunkSize int, db *sql.DB, out chan<- []UnknownRowValues) error {
+	query := buildExtractQueryMssql(job, columns)
+	log.Debug("Query used to extract data from mssql: ", query)
+
+	rows, err := db.QueryContext(ctx, query)
+	if err != nil {
+		return err
+	}
+	defer rows.Close()
+
+	rowsChunk := make([]UnknownRowValues, 0, chunkSize)
+
+	for rows.Next() {
+		values := make([]any, len(columns))
+		scanArgs := make([]any, len(columns))
+
+		for i := range values {
+			scanArgs[i] = &values[i]
+		}
+
+		if err := rows.Scan(scanArgs...); err != nil {
+			return err
+		}
+
+		rowsChunk = append(rowsChunk, values)
+
+		if len(rowsChunk) >= chunkSize {
+			out <- rowsChunk
+			rowsChunk = make([]UnknownRowValues, 0, chunkSize)
+			log.Infof("Chunk send... %+v", job)
+		}
+	}
+
+	if len(rowsChunk) > 0 {
+		out <- rowsChunk
+		log.Infof("Chunk send... %+v", job)
+	}
+
+	return nil
+}