refactor: update GenericLoader to use ProcessBatchWithRetries; enhance error handling and retry logic

cmd/go_migrate/process.go

@@ -13,6 +13,7 @@ import (
 	dbwrapper "git.ksdemosapps.com/kylesoda/go-migrate/internal/app/db-wrapper"
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/etl"
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/etl/extractors"
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/etl/loaders"
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/etl/table_analyzers"
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/etl/transformers"
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/models"
@@ -43,7 +44,7 @@ func processMigrationJob(
 	targetTableAnalyzer etl.TableAnalyzer,
 	extractor extractors.GenericExtractor,
 	azureClient *azure.Client,
-	loader etl.Loader,
+	loader loaders.GenericLoader,
 	job config.Job,
 	targetDbType string,
 ) models.JobResult {
@@ -158,6 +159,7 @@ func processMigrationJob(
 				chJobErrors,
 				&wgActivePartitions,
 				&rowsRead,
+				job.SourceTable.FromJsonColumns,
 			)
 		})
 	}
@@ -188,12 +190,12 @@ func processMigrationJob(
 
 	for range job.MaxLoaders {
 		wgLoaders.Go(func() {
-			loader.Exec(
+			loader.Consume(
 				localCtx,
 				job.TargetTable,
 				targetColTypes,
+				job.Retry,
 				chBatchesTransformed,
-				chLoadersErrors,
 				chJobErrors,
 				&wgActiveBatches,
 				&rowsLoaded,

config.yaml

@@ -46,6 +46,9 @@ jobs:
       schema: Red
       table: PUERTO
       primary_key: ID_PUERTO
+      from_json:
+        - column: $node_id*
+          field: id
     target:
       schema: Red
       table: PUERTO

internal/app/config/migration.go

@@ -43,6 +43,11 @@ type JobConfig struct {
 	ToStorage               ToStorageConfig `yaml:"to_storage"`
 }
 
+type FromJsonItem struct {
+	Column string `yaml:"column"`
+	Field  string `yaml:"field"`
+}
+
 type TableInfo struct {
 	Schema string `yaml:"schema"`
 	Table  string `yaml:"table"`
@@ -51,6 +56,7 @@ type TableInfo struct {
 type SourceTableInfo struct {
 	TableInfo       `yaml:",inline"`
 	PrimaryKey      string         `yaml:"primary_key"`
+	FromJsonColumns []FromJsonItem `yaml:"from_json"`
 }
 
 type TargetTableInfo struct {

internal/app/db-wrapper/mssql.go

@@ -6,8 +6,11 @@ import (
 	"fmt"
 	"strings"
 
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/config"
 	dbdialects "git.ksdemosapps.com/kylesoda/go-migrate/internal/app/db-wrapper/db_dialects"
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/models"
 	mssql "github.com/microsoft/go-mssqldb"
+	"github.com/sirupsen/logrus"
 )
 
 func init() {
@@ -177,27 +180,57 @@ func (mw *mssqlDbWrapper) SaveMassive(ctx context.Context, schema string, table
 	return rowsAffected, nil
 }
 
-func (mw *mssqlDbWrapper) QueryFromObject(ctx context.Context, q ExtractionQuery) (RowsResult, error) {
+func buildExtractQueryMssql(q ExtractionQuery) (string, error) {
 	var sbQuery strings.Builder
 
 	sbQuery.WriteString("SELECT ")
 
-	if len(q.Columns) == 0 {
-		sbQuery.WriteString("*")
-	} else {
-		for i, col := range q.Columns {
-			fmt.Fprintf(&sbQuery, "[%s]", col.Name())
+	hasRegularColumns := len(q.Columns) > 0
+	hasJsonColumns := len(q.FromJsonColumns) > 0
 
+	// logrus.Debugf("Extraction query: %+v", q)
+
+	resolvedJson := make(map[string][]config.FromJsonItem, len(q.FromJsonColumns))
+	if hasJsonColumns {
+		for _, jsonConfig := range q.FromJsonColumns {
+			actualColumnName, err := findColumnByPattern(q.Columns, jsonConfig.Column)
+			if err != nil {
+				return "", err
+			}
+			resolvedJson[actualColumnName] = append(resolvedJson[actualColumnName], jsonConfig)
+		}
+	}
+
+	selectParts := make([]string, 0, len(q.Columns)+len(q.FromJsonColumns))
+	if hasRegularColumns {
+		for _, col := range q.Columns {
+			jsonConfigs, isJsonColumn := resolvedJson[col.Name()]
+			if isJsonColumn {
+				for _, jsonConfig := range jsonConfigs {
+					jsonPath := buildJsonPathMssql(jsonConfig.Field)
+					jsonExpr := fmt.Sprintf("JSON_VALUE([%s], '%s') AS [%s]", col.Name(), jsonPath, col.Name())
+					selectParts = append(selectParts, jsonExpr)
+				}
+				continue
+			}
+
+			colExpr := fmt.Sprintf("[%s]", col.Name())
 			switch col.Type() {
 			case "GEOMETRY":
-				fmt.Fprintf(&sbQuery, ".STAsBinary() AS [%s]", col.Name())
+				colExpr = fmt.Sprintf("[%s].STAsBinary() AS [%s]", col.Name(), col.Name())
+			}
+			selectParts = append(selectParts, colExpr)
+		}
+	} else if !hasJsonColumns {
+		selectParts = append(selectParts, "*")
 	}
 
-			if i < len(q.Columns)-1 {
+	for i, part := range selectParts {
+		sbQuery.WriteString(part)
+		if i < len(selectParts)-1 {
 			sbQuery.WriteString(", ")
 		}
 	}
-	}
 
 	fmt.Fprintf(&sbQuery, " FROM [%s].[%s]", q.Schema, q.Table)
 
@@ -231,9 +264,39 @@ func (mw *mssqlDbWrapper) QueryFromObject(ctx context.Context, q ExtractionQuery
 
 	fmt.Fprintf(&sbQuery, " ORDER BY [%s] ASC", q.PrimaryKey)
 
-	queryString := sbQuery.String()
+	return sbQuery.String(), nil
+}
 
-	// logrus.Debugf("Query: %s", queryString)
+func findColumnByPattern(columns []models.ColumnType, pattern string) (string, error) {
+	if pattern == "" {
+		return "", fmt.Errorf("column pattern cannot be empty")
+	}
+
+	if before, ok := strings.CutSuffix(pattern, "*"); ok {
+		prefix := before
+		for _, col := range columns {
+			if strings.HasPrefix(col.Name(), prefix) {
+				return col.Name(), nil
+			}
+		}
+		return "", fmt.Errorf("no column found matching pattern '%s'", pattern)
+	}
+
+	for _, col := range columns {
+		if col.Name() == pattern {
+			return col.Name(), nil
+		}
+	}
+	return "", fmt.Errorf("column '%s' not found in table columns", pattern)
+}
+
+func (mw *mssqlDbWrapper) QueryFromObject(ctx context.Context, q ExtractionQuery) (RowsResult, error) {
+	queryString, err := buildExtractQueryMssql(q)
+	if err != nil {
+		return nil, err
+	}
+
+	logrus.Debugf("Query: %s", queryString)
 
 	var queryArgs []any
 
@@ -247,3 +310,11 @@ func (mw *mssqlDbWrapper) QueryFromObject(ctx context.Context, q ExtractionQuery
 
 	return mw.Query(ctx, queryString, queryArgs...)
 }
+
+func buildJsonPathMssql(field string) string {
+	if len(field) > 0 && field[0] == '.' {
+		field = field[1:]
+	}
+
+	return "$." + field
+}

internal/app/db-wrapper/mssql_test.go

@@ -0,0 +1,396 @@
+package dbwrapper
+
+import (
+	"strings"
+	"testing"
+
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/config"
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/models"
+)
+
+func TestBuildExtractQueryMssql_NoJsonColumns(t *testing.T) {
+	q := ExtractionQuery{
+		Schema:     "dbo",
+		Table:      "Users",
+		PrimaryKey: "ID",
+		Columns: []models.ColumnType{
+			models.NewColumnType("ID", false, false, "INT", "int", "INT", false, 0, 0, 0),
+			models.NewColumnType("Name", true, false, "VARCHAR", "varchar", "VARCHAR", true, 255, 0, 0),
+		},
+		FromJsonColumns: []config.FromJsonItem{},
+		LowerLimit:      ExtractorQueryLimit{IsValid: false},
+		UpperLimit:      ExtractorQueryLimit{IsValid: false},
+	}
+
+	query, err := buildExtractQueryMssql(q)
+	if err != nil {
+		t.Fatalf("Expected no error, got: %v", err)
+	}
+
+	if !strings.Contains(query, "SELECT [ID], [Name]") {
+		t.Errorf("Expected columns in query, got: %s", query)
+	}
+
+	if !strings.Contains(query, "FROM [dbo].[Users]") {
+		t.Errorf("Expected FROM clause, got: %s", query)
+	}
+
+	if !strings.Contains(query, "ORDER BY [ID] ASC") {
+		t.Errorf("Expected ORDER BY clause, got: %s", query)
+	}
+}
+
+func TestBuildExtractQueryMssql_WithJsonColumns_ExactColumnMatch(t *testing.T) {
+	// Test that the actual column name is used as alias, not a generated one
+	q := ExtractionQuery{
+		Schema:     "dbo",
+		Table:      "Events",
+		PrimaryKey: "EventID",
+		Columns: []models.ColumnType{
+			models.NewColumnType("EventID", false, false, "INT", "int", "INT", false, 0, 0, 0),
+			models.NewColumnType("EventData", true, false, "VARCHAR", "varchar", "VARCHAR", true, 500, 0, 0),
+		},
+		FromJsonColumns: []config.FromJsonItem{
+			{Column: "EventData", Field: ".userId"},
+			{Column: "EventData", Field: ".timestamp"},
+		},
+		LowerLimit: ExtractorQueryLimit{IsValid: false},
+		UpperLimit: ExtractorQueryLimit{IsValid: false},
+	}
+
+	query, err := buildExtractQueryMssql(q)
+	if err != nil {
+		t.Fatalf("Expected no error, got: %v", err)
+	}
+
+	if !strings.HasPrefix(query, "SELECT [EventID], JSON_VALUE([EventData], '$.userId') AS [EventData], JSON_VALUE([EventData], '$.timestamp') AS [EventData]") {
+		t.Errorf("Expected JSON columns to replace EventData in-order, got: %s", query)
+	}
+
+	if strings.Contains(query, "SELECT [EventID], [EventData]") {
+		t.Errorf("Expected EventData to be replaced by JSON extraction, got: %s", query)
+	}
+
+	// Alias should be exactly "EventData", not "EventData_userId"
+	if !strings.Contains(query, "JSON_VALUE([EventData], '$.userId') AS [EventData]") {
+		t.Errorf("Expected JSON alias to be [EventData], got: %s", query)
+	}
+
+	if !strings.Contains(query, "JSON_VALUE([EventData], '$.timestamp') AS [EventData]") {
+		t.Errorf("Expected JSON alias to be [EventData], got: %s", query)
+	}
+
+	// Should have comma separating them
+	if !strings.Contains(query, "JSON_VALUE([EventData], '$.userId') AS [EventData], JSON_VALUE([EventData], '$.timestamp') AS [EventData]") {
+		t.Errorf("Expected comma-separated JSON values, got: %s", query)
+	}
+}
+
+func TestBuildExtractQueryMssql_WithWildcardPattern(t *testing.T) {
+	// Test that wildcard pattern matching finds the correct column
+	q := ExtractionQuery{
+		Schema:     "dbo",
+		Table:      "Events",
+		PrimaryKey: "ID",
+		Columns: []models.ColumnType{
+			models.NewColumnType("ID", false, false, "INT", "int", "INT", false, 0, 0, 0),
+			models.NewColumnType("NodeMetadata", true, false, "VARCHAR", "varchar", "VARCHAR", true, 500, 0, 0),
+		},
+		FromJsonColumns: []config.FromJsonItem{
+			{Column: "NodeMeta*", Field: ".id"},
+		},
+		LowerLimit: ExtractorQueryLimit{IsValid: false},
+		UpperLimit: ExtractorQueryLimit{IsValid: false},
+	}
+
+	query, err := buildExtractQueryMssql(q)
+	if err != nil {
+		t.Fatalf("Expected no error, got: %v", err)
+	}
+
+	// Should find "NodeMetadata" from pattern "NodeMeta*" and use it as alias
+	if !strings.Contains(query, "JSON_VALUE([NodeMetadata], '$.id') AS [NodeMetadata]") {
+		t.Errorf("Expected to find and use NodeMetadata column by pattern, got: %s", query)
+	}
+
+	if strings.Contains(query, "SELECT [ID], [NodeMetadata]") {
+		t.Errorf("Expected NodeMetadata to be replaced by JSON extraction, got: %s", query)
+	}
+}
+
+func TestBuildExtractQueryMssql_ColumnNotFound_Error(t *testing.T) {
+	// Test that an error is returned when column is not found
+	q := ExtractionQuery{
+		Schema:     "dbo",
+		Table:      "Events",
+		PrimaryKey: "ID",
+		Columns: []models.ColumnType{
+			models.NewColumnType("ID", false, false, "INT", "int", "INT", false, 0, 0, 0),
+		},
+		FromJsonColumns: []config.FromJsonItem{
+			{Column: "NonExistentColumn", Field: ".id"},
+		},
+		LowerLimit: ExtractorQueryLimit{IsValid: false},
+		UpperLimit: ExtractorQueryLimit{IsValid: false},
+	}
+
+	query, err := buildExtractQueryMssql(q)
+	if err == nil {
+		t.Fatalf("Expected error for missing column, got no error. Query: %s", query)
+	}
+
+	if !strings.Contains(err.Error(), "NonExistentColumn") {
+		t.Errorf("Expected error message to contain column name, got: %v", err)
+	}
+}
+
+func TestBuildExtractQueryMssql_WildcardPatternNotMatched_Error(t *testing.T) {
+	// Test that an error is returned when wildcard pattern doesn't match any column
+	q := ExtractionQuery{
+		Schema:     "dbo",
+		Table:      "Events",
+		PrimaryKey: "ID",
+		Columns: []models.ColumnType{
+			models.NewColumnType("ID", false, false, "INT", "int", "INT", false, 0, 0, 0),
+			models.NewColumnType("EventData", true, false, "VARCHAR", "varchar", "VARCHAR", true, 500, 0, 0),
+		},
+		FromJsonColumns: []config.FromJsonItem{
+			{Column: "NonMatching*", Field: ".id"},
+		},
+		LowerLimit: ExtractorQueryLimit{IsValid: false},
+		UpperLimit: ExtractorQueryLimit{IsValid: false},
+	}
+
+	query, err := buildExtractQueryMssql(q)
+	if err == nil {
+		t.Fatalf("Expected error for non-matching wildcard pattern, got no error. Query: %s", query)
+	}
+
+	if !strings.Contains(err.Error(), "NonMatching*") {
+		t.Errorf("Expected error message to contain pattern, got: %v", err)
+	}
+}
+
+func TestBuildExtractQueryMssql_NestedJsonFields(t *testing.T) {
+	q := ExtractionQuery{
+		Schema:     "dbo",
+		Table:      "Data",
+		PrimaryKey: "ID",
+		Columns: []models.ColumnType{
+			models.NewColumnType("ID", false, false, "INT", "int", "INT", false, 0, 0, 0),
+			models.NewColumnType("NodeData", true, false, "VARCHAR", "varchar", "VARCHAR", true, 500, 0, 0),
+		},
+		FromJsonColumns: []config.FromJsonItem{
+			{Column: "NodeData", Field: ".user.name"},
+			{Column: "NodeData", Field: ".user.email"},
+		},
+		LowerLimit: ExtractorQueryLimit{IsValid: false},
+		UpperLimit: ExtractorQueryLimit{IsValid: false},
+	}
+
+	query, err := buildExtractQueryMssql(q)
+	if err != nil {
+		t.Fatalf("Expected no error, got: %v", err)
+	}
+
+	if !strings.Contains(query, "JSON_VALUE([NodeData], '$.user.name') AS [NodeData]") {
+		t.Errorf("Expected nested JSON path for user.name, got: %s", query)
+	}
+
+	if !strings.Contains(query, "JSON_VALUE([NodeData], '$.user.email') AS [NodeData]") {
+		t.Errorf("Expected nested JSON path for user.email, got: %s", query)
+	}
+
+	if strings.Contains(query, "SELECT [ID], [NodeData]") {
+		t.Errorf("Expected NodeData to be replaced by JSON extraction, got: %s", query)
+	}
+}
+
+func TestBuildExtractQueryMssql_WithRangeLimits(t *testing.T) {
+	q := ExtractionQuery{
+		Schema:     "dbo",
+		Table:      "Products",
+		PrimaryKey: "ProductID",
+		Columns: []models.ColumnType{
+			models.NewColumnType("ProductID", false, false, "INT", "int", "INT", false, 0, 0, 0),
+			models.NewColumnType("Details", true, false, "VARCHAR", "varchar", "VARCHAR", true, 500, 0, 0),
+		},
+		FromJsonColumns: []config.FromJsonItem{
+			{Column: "Details", Field: ".price"},
+		},
+		LowerLimit: ExtractorQueryLimit{IsValid: true, IsInclusive: true, Value: 100},
+		UpperLimit: ExtractorQueryLimit{IsValid: true, IsInclusive: false, Value: 500},
+	}
+
+	query, err := buildExtractQueryMssql(q)
+	if err != nil {
+		t.Fatalf("Expected no error, got: %v", err)
+	}
+
+	if !strings.Contains(query, "WHERE [ProductID] >= @min") {
+		t.Errorf("Expected WHERE clause with >=, got: %s", query)
+	}
+
+	if !strings.Contains(query, "[ProductID] < @max") {
+		t.Errorf("Expected upper limit with <, got: %s", query)
+	}
+
+	if !strings.Contains(query, "JSON_VALUE([Details], '$.price') AS [Details]") {
+		t.Errorf("Expected JSON_VALUE for Details, got: %s", query)
+	}
+
+	if strings.Contains(query, "SELECT [ProductID], [Details]") {
+		t.Errorf("Expected Details to be replaced by JSON extraction, got: %s", query)
+	}
+}
+
+func TestBuildJsonPathMssql(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{".id", "$.id"},
+		{"id", "$.id"},
+		{".user.name", "$.user.name"},
+		{"user.name", "$.user.name"},
+		{".location.coordinates.lat", "$.location.coordinates.lat"},
+		{"", "$."},
+	}
+
+	for _, tt := range tests {
+		result := buildJsonPathMssql(tt.input)
+		if result != tt.expected {
+			t.Errorf("buildJsonPathMssql(%q) = %q, want %q", tt.input, result, tt.expected)
+		}
+	}
+}
+
+func TestFindColumnByPattern_ExactMatch(t *testing.T) {
+	columns := []models.ColumnType{
+		models.NewColumnType("ID", false, false, "INT", "int", "INT", false, 0, 0, 0),
+		models.NewColumnType("Metadata", true, false, "VARCHAR", "varchar", "VARCHAR", true, 500, 0, 0),
+		models.NewColumnType("EventData", true, false, "VARCHAR", "varchar", "VARCHAR", true, 500, 0, 0),
+	}
+
+	result, err := findColumnByPattern(columns, "Metadata")
+	if err != nil {
+		t.Fatalf("Expected no error, got: %v", err)
+	}
+
+	if result != "Metadata" {
+		t.Errorf("Expected 'Metadata', got '%s'", result)
+	}
+}
+
+func TestFindColumnByPattern_WildcardMatch(t *testing.T) {
+	columns := []models.ColumnType{
+		models.NewColumnType("ID", false, false, "INT", "int", "INT", false, 0, 0, 0),
+		models.NewColumnType("NodeMetadata", true, false, "VARCHAR", "varchar", "VARCHAR", true, 500, 0, 0),
+		models.NewColumnType("EventData", true, false, "VARCHAR", "varchar", "VARCHAR", true, 500, 0, 0),
+	}
+
+	result, err := findColumnByPattern(columns, "NodeMeta*")
+	if err != nil {
+		t.Fatalf("Expected no error, got: %v", err)
+	}
+
+	if result != "NodeMetadata" {
+		t.Errorf("Expected 'NodeMetadata', got '%s'", result)
+	}
+}
+
+func TestFindColumnByPattern_NotFound(t *testing.T) {
+	columns := []models.ColumnType{
+		models.NewColumnType("ID", false, false, "INT", "int", "INT", false, 0, 0, 0),
+		models.NewColumnType("Metadata", true, false, "VARCHAR", "varchar", "VARCHAR", true, 500, 0, 0),
+	}
+
+	result, err := findColumnByPattern(columns, "NonExistent")
+	if err == nil {
+		t.Fatalf("Expected error, got no error. Result: %s", result)
+	}
+
+	if !strings.Contains(err.Error(), "NonExistent") {
+		t.Errorf("Expected error to contain column name, got: %v", err)
+	}
+}
+
+func TestFindColumnByPattern_WildcardNotFound(t *testing.T) {
+	columns := []models.ColumnType{
+		models.NewColumnType("ID", false, false, "INT", "int", "INT", false, 0, 0, 0),
+		models.NewColumnType("Metadata", true, false, "VARCHAR", "varchar", "VARCHAR", true, 500, 0, 0),
+	}
+
+	result, err := findColumnByPattern(columns, "Event*")
+	if err == nil {
+		t.Fatalf("Expected error, got no error. Result: %s", result)
+	}
+
+	if !strings.Contains(err.Error(), "Event*") {
+		t.Errorf("Expected error to contain pattern, got: %v", err)
+	}
+}
+
+func TestBuildExtractQueryMssql_OnlyJsonColumns(t *testing.T) {
+	// Test when all columns are used via JSON extraction
+	q := ExtractionQuery{
+		Schema:     "dbo",
+		Table:      "Data",
+		PrimaryKey: "ID",
+		Columns: []models.ColumnType{
+			models.NewColumnType("ID", false, false, "INT", "int", "INT", false, 0, 0, 0),
+			models.NewColumnType("JsonData", true, false, "VARCHAR", "varchar", "VARCHAR", true, 500, 0, 0),
+		},
+		FromJsonColumns: []config.FromJsonItem{
+			{Column: "JsonData", Field: ".field1"},
+		},
+		LowerLimit: ExtractorQueryLimit{IsValid: false},
+		UpperLimit: ExtractorQueryLimit{IsValid: false},
+	}
+
+	query, err := buildExtractQueryMssql(q)
+	if err != nil {
+		t.Fatalf("Expected no error, got: %v", err)
+	}
+
+	if !strings.HasPrefix(query, "SELECT [ID], JSON_VALUE([JsonData], '$.field1') AS [JsonData]") {
+		t.Errorf("Expected JsonData to be replaced by JSON extraction, got: %s", query)
+	}
+
+	if strings.Contains(query, "SELECT [ID], [JsonData]") {
+		t.Errorf("Expected JsonData to be excluded from raw selection, got: %s", query)
+	}
+}
+
+func TestBuildExtractQueryMssql_JsonColumnsReplaceInOrder(t *testing.T) {
+	q := ExtractionQuery{
+		Schema:     "dbo",
+		Table:      "Users",
+		PrimaryKey: "UserID",
+		Columns: []models.ColumnType{
+			models.NewColumnType("UserID", false, false, "INT", "int", "INT", false, 0, 0, 0),
+			models.NewColumnType("Name", true, false, "VARCHAR", "varchar", "VARCHAR", false, 255, 0, 0),
+			models.NewColumnType("Email", true, false, "VARCHAR", "varchar", "VARCHAR", false, 255, 0, 0),
+			models.NewColumnType("Metadata", true, false, "NVARCHAR", "nvarchar", "NVARCHAR", true, 4000, 0, 0),
+			models.NewColumnType("Profile", true, false, "NVARCHAR", "nvarchar", "NVARCHAR", true, 4000, 0, 0),
+			models.NewColumnType("Settings", true, false, "NVARCHAR", "nvarchar", "NVARCHAR", true, 4000, 0, 0),
+		},
+		FromJsonColumns: []config.FromJsonItem{
+			{Column: "Metadata", Field: ".id"},
+			{Column: "Profile", Field: ".id"},
+			{Column: "Settings", Field: ".id"},
+		},
+		LowerLimit: ExtractorQueryLimit{IsValid: false},
+		UpperLimit: ExtractorQueryLimit{IsValid: false},
+	}
+
+	query, err := buildExtractQueryMssql(q)
+	if err != nil {
+		t.Fatalf("Expected no error, got: %v", err)
+	}
+
+	expected := "SELECT [UserID], [Name], [Email], JSON_VALUE([Metadata], '$.id') AS [Metadata], JSON_VALUE([Profile], '$.id') AS [Profile], JSON_VALUE([Settings], '$.id') AS [Settings] FROM [dbo].[Users] ORDER BY [UserID] ASC"
+	if query != expected {
+		t.Errorf("Unexpected query.\nExpected: %s\nGot: %s", expected, query)
+	}
+}

internal/app/db-wrapper/types.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/config"
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/models"
 )
 
@@ -39,6 +40,7 @@ type ExtractionQuery struct {
 	Columns         []models.ColumnType
 	LowerLimit      ExtractorQueryLimit
 	UpperLimit      ExtractorQueryLimit
+	FromJsonColumns []config.FromJsonItem
 }
 
 type DbWrapper interface {

internal/app/etl/extractors/consume.go

@@ -25,6 +25,7 @@ func (ex *GenericExtractor) Consume(
 	chErrorsOut chan<- custom_errors.JobError,
 	wgActivePartitions *sync.WaitGroup,
 	rowsRead *int64,
+	fromJsonColumns []config.FromJsonItem,
 ) {
 	indexPrimaryKey := slices.IndexFunc(columns, func(col models.ColumnType) bool {
 		return strings.EqualFold(col.Name(), tableInfo.PrimaryKey)
@@ -65,6 +66,7 @@ func (ex *GenericExtractor) Consume(
 				indexPrimaryKey,
 				retryConfig,
 				chBatchesOut,
+				fromJsonColumns,
 			)
 			wgActivePartitions.Done()
 

internal/app/etl/extractors/process-with-retries.go

@@ -22,6 +22,7 @@ func (ex *GenericExtractor) ProcessPartitionWithRetries(
 	indexPrimaryKey int,
 	retryConfig config.RetryConfig,
 	chBatchesOut chan<- models.Batch,
+	fromJsonColumns []config.FromJsonItem,
 ) (int64, error) {
 	var totalRowsRead int64
 	currentParitition := partition
@@ -35,6 +36,7 @@ func (ex *GenericExtractor) ProcessPartitionWithRetries(
 			currentParitition,
 			indexPrimaryKey,
 			chBatchesOut,
+			fromJsonColumns,
 		)
 		// logrus.Debugf("Partition %v finished processing (%s.%s)", partition.Id, tableInfo.Schema, tableInfo.Table)
 		totalRowsRead += rowsRead

internal/app/etl/extractors/process.go

@@ -47,6 +47,7 @@ func (ex *GenericExtractor) ProcessPartition(
 	partition models.Partition,
 	indexPrimaryKey int,
 	chBatchesOut chan<- models.Batch,
+	fromJsonColumns []config.FromJsonItem,
 ) (int64, error) {
 	query := dbwrapper.ExtractionQuery{
 		Schema:     tableInfo.Schema,
@@ -63,6 +64,7 @@ func (ex *GenericExtractor) ProcessPartition(
 			IsInclusive: partition.Range.IsMaxInclusive,
 			Value:       partition.Range.Max,
 		},
+		FromJsonColumns: fromJsonColumns,
 	}
 
 	// logrus.Debugf("Processing partition: %+v (%s.%s)", query, tableInfo.Schema, tableInfo.Table)

internal/app/etl/loaders/consume.go

@@ -38,7 +38,7 @@ func (gl *GenericLoader) Consume(
 				return
 			}
 
-			processedRows, err := gl.ProcessBatch(ctx, tableInfo, colNames, batch)
+			processedRows, err := gl.ProcessBatchWithRetries(ctx, tableInfo, colNames, retryConfig, batch)
 			wgActiveBatches.Done()
 
 			if err != nil {

internal/app/etl/loaders/main.go

@@ -1,116 +1,13 @@
 package loaders
 
 import (
-	"context"
-	"errors"
-	"fmt"
-	"sync"
-	"sync/atomic"
-
-	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/config"
-	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/custom_errors"
 	dbwrapper "git.ksdemosapps.com/kylesoda/go-migrate/internal/app/db-wrapper"
-	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/etl"
-	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/models"
-	"github.com/jackc/pgx/v5/pgconn"
 )
 
 type GenericLoader struct {
 	db dbwrapper.DbWrapper
 }
 
-func NewGenericLoader(db dbwrapper.DbWrapper) etl.Loader {
-	return &GenericLoader{db: db}
-}
-
-func (gl *GenericLoader) ProcessBatch(
-	ctx context.Context,
-	tableInfo config.TargetTableInfo,
-	colNames []string,
-	batch models.Batch,
-) (int, error) {
-	_, err := gl.db.SaveMassive(
-		ctx,
-		tableInfo.Schema,
-		tableInfo.Table,
-		colNames,
-		batch.Rows,
-	)
-
-	if err != nil {
-		if pgErr, ok := errors.AsType[*pgconn.PgError](err); ok {
-			if pgErr.Code == "23505" {
-				return 0, &custom_errors.JobError{
-					ShouldCancelJob: true,
-					Msg:             fmt.Sprintf("Fatal error in table %s.%s", tableInfo.Schema, tableInfo.Table),
-					Prev:            err,
-				}
-			}
-		}
-
-		return 0, &custom_errors.LoaderError{Batch: batch, Msg: err.Error()}
-	}
-
-	return len(batch.Rows), nil
-}
-
-func (gl *GenericLoader) Exec(
-	ctx context.Context,
-	tableInfo config.TargetTableInfo,
-	columns []models.ColumnType,
-	chBatchesIn <-chan models.Batch,
-	chErrorsOut chan<- custom_errors.LoaderError,
-	chJobErrorsOut chan<- custom_errors.JobError,
-	wgActiveBatches *sync.WaitGroup,
-	rowsLoaded *int64,
-) {
-	colNames := mapSlice(columns, func(col models.ColumnType) string {
-		return col.Name()
-	})
-
-	for {
-		if ctx.Err() != nil {
-			return
-		}
-
-		select {
-		case <-ctx.Done():
-			return
-		case batch, ok := <-chBatchesIn:
-			if !ok {
-				return
-			}
-
-			processedRows, err := gl.ProcessBatch(ctx, tableInfo, colNames, batch)
-
-			if err != nil {
-				var ldError *custom_errors.LoaderError
-				var jobError *custom_errors.JobError
-				if errors.As(err, &ldError) {
-					select {
-					case <-ctx.Done():
-						return
-					case chErrorsOut <- *ldError:
-					}
-				} else if errors.As(err, &jobError) {
-					select {
-					case <-ctx.Done():
-						return
-					case chJobErrorsOut <- *jobError:
-					}
-				} else {
-					select {
-					case <-ctx.Done():
-						return
-					case chErrorsOut <- custom_errors.LoaderError{Batch: batch, Msg: err.Error()}:
-					}
-				}
-
-				continue
-			}
-
-			wgActiveBatches.Done()
-			atomic.AddInt64(rowsLoaded, int64(processedRows))
-		}
-	}
+func NewGenericLoader(db dbwrapper.DbWrapper) GenericLoader {
+	return GenericLoader{db: db}
 }

internal/app/etl/loaders/process-with-retries.go

@@ -0,0 +1,50 @@
+package loaders
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/config"
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/custom_errors"
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/models"
+)
+
+func (gl *GenericLoader) ProcessBatchWithRetries(
+	ctx context.Context,
+	tableInfo config.TargetTableInfo,
+	colNames []string,
+	retryConfig config.RetryConfig,
+	batch models.Batch,
+) (int64, error) {
+	for {
+		rowsLoaded, err := gl.ProcessBatch(ctx, tableInfo, colNames, batch)
+		if err == nil {
+			return rowsLoaded, nil
+		}
+
+		if btError, ok := errors.AsType[*custom_errors.LoaderError](err); ok {
+			batch.RetryCounter++
+
+			if batch.RetryCounter >= retryConfig.Attempts {
+				return rowsLoaded, &custom_errors.JobError{
+					ShouldCancelJob: false,
+					Msg:             fmt.Sprintf("Temporal error in batch %v (retries: %d)", btError.Batch.Id, btError.Batch.RetryCounter),
+					Prev:            btError,
+				}
+			}
+
+			delay := custom_errors.ComputeBackoffDelay(
+				batch.RetryCounter,
+				retryConfig.BaseDelayMs,
+				retryConfig.MaxDelayMs,
+				retryConfig.MaxJitterMs,
+			)
+			time.Sleep(delay)
+			continue
+		}
+
+		return rowsLoaded, err
+	}
+}

internal/app/etl/loaders/process.go

@@ -0,0 +1,43 @@
+package loaders
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/config"
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/custom_errors"
+	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/models"
+	"github.com/jackc/pgx/v5/pgconn"
+)
+
+func (gl *GenericLoader) ProcessBatch(
+	ctx context.Context,
+	tableInfo config.TargetTableInfo,
+	colNames []string,
+	batch models.Batch,
+) (int64, error) {
+	_, err := gl.db.SaveMassive(
+		ctx,
+		tableInfo.Schema,
+		tableInfo.Table,
+		colNames,
+		batch.Rows,
+	)
+
+	if err != nil {
+		if pgErr, ok := errors.AsType[*pgconn.PgError](err); ok {
+			if pgErr.Code == "23505" {
+				return 0, &custom_errors.JobError{
+					ShouldCancelJob: true,
+					Msg:             fmt.Sprintf("Fatal error in table %s.%s", tableInfo.Schema, tableInfo.Table),
+					Prev:            err,
+				}
+			}
+		}
+
+		return 0, &custom_errors.LoaderError{Batch: batch, Msg: err.Error()}
+	}
+
+	return int64(len(batch.Rows)), nil
+}

internal/app/etl/types.go

@@ -51,18 +51,7 @@ type Loader interface {
 		tableInfo config.TargetTableInfo,
 		colNames []string,
 		batch models.Batch,
-	) (int, error)
-
-	Exec(
-		ctx context.Context,
-		tableInfo config.TargetTableInfo,
-		columns []models.ColumnType,
-		chBatchesIn <-chan models.Batch,
-		chErrorsOut chan<- custom_errors.LoaderError,
-		chJobErrorsOut chan<- custom_errors.JobError,
-		wgActiveBatches *sync.WaitGroup,
-		rowsLoaded *int64,
-	)
+	) (int64, error)
 }
 
 type TableAnalyzer interface {