feat: enhance column type querying functions for improved error handling and SQL compatibility

cmd/go_migrate/connect.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"database/sql"
+	"errors"
 	"fmt"
 	"sync"
 	"time"
@@ -69,7 +70,7 @@ func connectToDatabases() (*sql.DB, *pgxpool.Pool, error) {
 	wg.Wait()
 
 	if sourceDbErr != nil || targetDbErr != nil {
-		return nil, nil, fmt.Errorf("Unable to connect to databases: %w (source), %w (target)", sourceDbErr, targetDbErr)
+		return nil, nil, errors.New("Unable to connect to databases")
 	}
 
 	return sourceDb, targetDb, nil

cmd/go_migrate/main.go

@@ -3,12 +3,12 @@ package main
 import (
 	"context"
 	"database/sql"
+	"errors"
 	"fmt"
 
 	"sync"
 	"time"
 
-	"github.com/jackc/pgx/v5/pgconn"
 	"github.com/jackc/pgx/v5/pgxpool"
 	_ "github.com/microsoft/go-mssqldb"
 	log "github.com/sirupsen/logrus"
@@ -52,53 +52,127 @@ func main() {
 	log.Info("Migration completed successfully!")
 }
 
-func querySourceColTypes(db *sql.DB, migrationJob MigrationJob) ([]sql.ColumnType, error) {
+func querySourceColTypes(db *sql.DB, migrationJob MigrationJob) ([]ColumnType, error) {
-	query := fmt.Sprintf(`SELECT * FROM [%s].[%s] WHERE 0 = 1`, migrationJob.Schema, migrationJob.Table)
+	query := `
+SELECT 
+	c.name AS name,
+	t.name AS user_type,
+	CASE WHEN t.is_user_defined = 0 THEN t.name ELSE bt.name END AS system_type,
+	c.is_nullable AS nullable,
+	c.max_length AS max_length,
+	c.precision AS precision,
+	c.scale AS scale
+FROM sys.columns c
+JOIN sys.types t ON c.user_type_id = t.user_type_id
+LEFT JOIN sys.types bt ON t.is_user_defined = 1 AND bt.user_type_id = t.system_type_id
+JOIN sys.tables st ON c.object_id = st.object_id
+JOIN sys.schemas s ON st.schema_id = s.schema_id
+WHERE s.name = @schema AND st.name = @table
+ORDER BY c.column_id;
+`
 
 	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
 	defer cancel()
 
-	rows, err := db.QueryContext(ctx, query)
+	rows, err := db.QueryContext(ctx, query, sql.Named("schema", migrationJob.Schema), sql.Named("table", migrationJob.Table))
 	if err != nil {
 		return nil, fmt.Errorf("Error querying column types: %w", err)
 	}
 	defer rows.Close()
 
-	colTypesPointers, err := rows.ColumnTypes()
+	var colTypes []ColumnType
-	if err != nil {
+
-		return nil, err
+	for rows.Next() {
+		var column ColumnType
+
+		if err := rows.Scan(
+			&column.name,
+			&column.userType,
+			&column.systemType,
+			&column.nullable,
+			&column.maxLength,
+			&column.precision,
+			&column.scale,
+		); err != nil {
+			return nil, fmt.Errorf("Error scanning column type results: %W", err)
 		}
 
-	colTypes := make([]sql.ColumnType, 0, len(colTypesPointers))
+		colTypes = append(colTypes, column)
-	for _, c := range colTypesPointers {
-		colTypes = append(colTypes, *c)
 	}
 
 	return colTypes, nil
 }
 
-func queryTargetColTypes(db *pgxpool.Pool, migrationJob MigrationJob) ([]pgconn.FieldDescription, error) {
+func queryTargetColTypes(db *pgxpool.Pool, migrationJob MigrationJob) ([]ColumnType, error) {
-	query := fmt.Sprintf(`SELECT * FROM "%s"."%s" WHERE 0 = 1`, migrationJob.Schema, migrationJob.Table)
+	query := `
+SELECT 
+  c.column_name AS name,
+  c.data_type AS user_type,
+  c.udt_name AS system_type,
+  (CASE WHEN c.is_nullable = 'YES' THEN TRUE ELSE FALSE END) AS nullable,
+  c.character_maximum_length AS max_length,
+  c.numeric_precision AS precision,
+  c.numeric_scale AS scale
+FROM information_schema.columns c
+WHERE c.table_schema = $1 AND c.table_name = $2
+ORDER BY c.ordinal_position;
+`
 
 	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
 	defer cancel()
 
-	rows, err := db.Query(ctx, query)
+	rows, err := db.Query(ctx, query, migrationJob.Schema, migrationJob.Table)
 	if err != nil {
 		return nil, fmt.Errorf("Error querying column types: %w", err)
 	}
 	defer rows.Close()
 
-	colTypes := rows.FieldDescriptions()
+	var colTypes []ColumnType
+
+	for rows.Next() {
+		var column ColumnType
+		var scanMaxLength *int64
+		var scanPrecision *int64
+		var scanScale *int64
+
+		if err := rows.Scan(
+			&column.name,
+			&column.userType,
+			&column.systemType,
+			&column.nullable,
+			&scanMaxLength,
+			&scanPrecision,
+			&scanScale,
+		); err != nil {
+			return nil, fmt.Errorf("Error scanning column type results: %w", err)
+		}
+
+		if scanMaxLength != nil {
+			column.maxLength = *scanMaxLength
+			column.hasMaxLength = true
+		} else {
+			column.maxLength = -1
+		}
+
+		if column.systemType == "decimal" {
+			if scanPrecision != nil && scanScale != nil {
+				column.precision = *scanPrecision
+				column.scale = *scanScale
+				column.hasPrecisionScale = true
+			}
+		}
+
+		colTypes = append(colTypes, column)
+	}
 
 	return colTypes, nil
 }
 
-func queryColumnTypes(sourceDb *sql.DB, targetDb *pgxpool.Pool, migrationJob MigrationJob) ([]sql.ColumnType, []pgconn.FieldDescription, error) {
+func queryColumnTypes(sourceDb *sql.DB, targetDb *pgxpool.Pool, migrationJob MigrationJob) ([]ColumnType, []ColumnType, error) {
 	var sourceDbErr error
 	var targetDbErr error
-	var sourceColTypes []sql.ColumnType
+	var sourceColTypes []ColumnType
-	var targetColTypes []pgconn.FieldDescription
+	var targetColTypes []ColumnType
 	var wg sync.WaitGroup
 
 	wg.Go(func() {
@@ -118,7 +192,7 @@ func queryColumnTypes(sourceDb *sql.DB, targetDb *pgxpool.Pool, migrationJob Mig
 	wg.Wait()
 
 	if sourceDbErr != nil || targetDbErr != nil {
-		return nil, nil, fmt.Errorf("Unable to connect to databases: %w (source), %w (target)", sourceDbErr, targetDbErr)
+		return nil, nil, errors.New("Error querying column types")
 	}
 
 	return sourceColTypes, targetColTypes, nil