Better handling of preloads

pkg/common/adapters/database/RELATION_LOADING.md

@@ -0,0 +1,218 @@
+# Automatic Relation Loading Strategies
+
+## Overview
+
+**NEW:** The database adapters now **automatically** choose the optimal loading strategy by inspecting your model's relationship tags!
+
+Simply use `PreloadRelation()` and the system automatically:
+- Detects relationship type from Bun/GORM tags
+- Uses **JOIN** for many-to-one and one-to-one (efficient, no duplication)
+- Uses **separate query** for one-to-many and many-to-many (avoids duplication)
+
+## How It Works
+
+```go
+// Just write this - the system handles the rest!
+db.NewSelect().
+    Model(&links).
+    PreloadRelation("Provider").  // ✓ Auto-detects belongs-to → uses JOIN
+    PreloadRelation("Tags").      // ✓ Auto-detects has-many → uses separate query
+    Scan(ctx, &links)
+```
+
+### Detection Logic
+
+The system inspects your model's struct tags:
+
+**Bun models:**
+```go
+type Link struct {
+    Provider   *Provider `bun:"rel:belongs-to"`   // → Detected: belongs-to → JOIN
+    Tags       []Tag     `bun:"rel:has-many"`     // → Detected: has-many → Separate query
+}
+```
+
+**GORM models:**
+```go
+type Link struct {
+    ProviderID int
+    Provider   *Provider `gorm:"foreignKey:ProviderID"`  // → Detected: belongs-to → JOIN
+    Tags       []Tag     `gorm:"many2many:link_tags"`    // → Detected: many-to-many → Separate query
+}
+```
+
+**Type inference (fallback):**
+- `[]Type` (slice) → has-many → Separate query
+- `*Type` (pointer) → belongs-to → JOIN
+- `Type` (struct) → belongs-to → JOIN
+
+### What Gets Logged
+
+Enable debug logging to see strategy selection:
+
+```go
+bunAdapter.EnableQueryDebug()
+```
+
+**Output:**
+```
+DEBUG: PreloadRelation 'Provider' detected as: belongs-to
+INFO:  Using JOIN strategy for belongs-to relation 'Provider'
+DEBUG: PreloadRelation 'Links' detected as: has-many
+DEBUG: Using separate query for has-many relation 'Links'
+```
+
+## Relationship Types
+
+| Bun Tag | GORM Pattern | Field Type | Strategy | Why |
+|---------|--------------|------------|----------|-----|
+| `rel:has-many` | Slice field | `[]Type` | Separate Query | Avoids duplicating parent data |
+| `rel:belongs-to` | `foreignKey:` | `*Type` | JOIN | Single parent, no duplication |
+| `rel:has-one` | Single pointer | `*Type` | JOIN | One-to-one, no duplication |
+| `rel:many-to-many` | `many2many:` | `[]Type` | Separate Query | Complex join, avoid cartesian |
+
+## Manual Override
+
+If you need to force a specific strategy, use `JoinRelation()`:
+
+```go
+// Force JOIN even for has-many (not recommended)
+db.NewSelect().
+    Model(&providers).
+    JoinRelation("Links").  // Explicitly use JOIN
+    Scan(ctx, &providers)
+```
+
+## Examples
+
+### Automatic Strategy Selection (Recommended)
+
+```go
+// Example 1: Loading parent provider for each link
+// System detects belongs-to → uses JOIN automatically
+db.NewSelect().
+    Model(&links).
+    PreloadRelation("Provider", func(q common.SelectQuery) common.SelectQuery {
+        return q.Where("active = ?", true)
+    }).
+    Scan(ctx, &links)
+
+// Generated SQL: Single query with JOIN
+// SELECT links.*, providers.*
+// FROM links
+// LEFT JOIN providers ON links.provider_id = providers.id
+// WHERE providers.active = true
+
+// Example 2: Loading child links for each provider
+// System detects has-many → uses separate query automatically
+db.NewSelect().
+    Model(&providers).
+    PreloadRelation("Links", func(q common.SelectQuery) common.SelectQuery {
+        return q.Where("active = ?", true)
+    }).
+    Scan(ctx, &providers)
+
+// Generated SQL: Two queries
+// Query 1: SELECT * FROM providers
+// Query 2: SELECT * FROM links
+//          WHERE provider_id IN (1, 2, 3, ...)
+//          AND active = true
+```
+
+### Mixed Relationships
+
+```go
+type Order struct {
+    ID         int
+    CustomerID int
+    Customer   *Customer `bun:"rel:belongs-to"`    // JOIN
+    Items      []Item    `bun:"rel:has-many"`      // Separate
+    Invoice    *Invoice  `bun:"rel:has-one"`       // JOIN
+}
+
+// All three handled optimally!
+db.NewSelect().
+    Model(&orders).
+    PreloadRelation("Customer").  // → JOIN (many-to-one)
+    PreloadRelation("Items").     // → Separate (one-to-many)
+    PreloadRelation("Invoice").   // → JOIN (one-to-one)
+    Scan(ctx, &orders)
+```
+
+## Performance Benefits
+
+### Before (Manual Strategy Selection)
+
+```go
+// You had to remember which to use:
+.PreloadRelation("Provider")  // Should I use PreloadRelation or JoinRelation?
+.PreloadRelation("Links")     // Which is more efficient here?
+```
+
+### After (Automatic Selection)
+
+```go
+// Just use PreloadRelation everywhere:
+.PreloadRelation("Provider")  // ✓ System uses JOIN automatically
+.PreloadRelation("Links")     // ✓ System uses separate query automatically
+```
+
+## Migration Guide
+
+**No changes needed!** If you're already using `PreloadRelation()`, it now automatically optimizes:
+
+```go
+// Before: Always used separate query
+.PreloadRelation("Provider")  // Inefficient: extra round trip
+
+// After: Automatic optimization
+.PreloadRelation("Provider")  // ✓ Now uses JOIN automatically!
+```
+
+## Implementation Details
+
+### Supported Bun Tags
+- `rel:has-many` → Separate query
+- `rel:belongs-to` → JOIN
+- `rel:has-one` → JOIN
+- `rel:many-to-many` or `rel:m2m` → Separate query
+
+### Supported GORM Patterns
+- `many2many:` tag → Separate query
+- `foreignKey:` tag → JOIN (belongs-to)
+- `[]Type` slice without many2many → Separate query (has-many)
+- `*Type` pointer with foreignKey → JOIN (belongs-to)
+- `*Type` pointer without foreignKey → JOIN (has-one)
+
+### Fallback Behavior
+- `[]Type` (slice) → Separate query (safe default for collections)
+- `*Type` or `Type` (single) → JOIN (safe default for single relations)
+- Unknown → Separate query (safest default)
+
+## Debugging
+
+To see strategy selection in action:
+
+```go
+// Enable debug logging
+bunAdapter.EnableQueryDebug()  // or gormAdapter.EnableQueryDebug()
+
+// Run your query
+db.NewSelect().
+    Model(&records).
+    PreloadRelation("RelationName").
+    Scan(ctx, &records)
+
+// Check logs for:
+// - "PreloadRelation 'X' detected as: belongs-to"
+// - "Using JOIN strategy for belongs-to relation 'X'"
+// - Actual SQL queries executed
+```
+
+## Best Practices
+
+1. **Use PreloadRelation() for everything** - Let the system optimize
+2. **Define proper relationship tags** - Ensures correct detection
+3. **Only use JoinRelation() for overrides** - When you know better than auto-detection
+4. **Enable debug logging during development** - Verify optimal strategies are chosen
+5. **Trust the system** - It's designed to choose correctly based on relationship type

pkg/common/adapters/database/bun.go

@@ -140,6 +140,8 @@ type BunSelectQuery struct {
 	tableName        string  // Just the table name, without schema
 	tableAlias       string
 	deferredPreloads []deferredPreload // Preloads to execute as separate queries
+	inJoinContext    bool              // Track if we're in a JOIN relation context
+	joinTableAlias   string            // Alias to use for JOIN conditions
 }
 
 // deferredPreload represents a preload that will be executed as a separate query
@@ -189,17 +191,67 @@ func (b *BunSelectQuery) ColumnExpr(query string, args ...interface{}) common.Se
 }
 
 func (b *BunSelectQuery) Where(query string, args ...interface{}) common.SelectQuery {
-	// If we have a table alias defined, check if the query references a different alias
+	// If we're in a JOIN context, add table prefix to unqualified columns
-	// This can happen in preloads where the user expects a certain alias but Bun generates another
+	if b.inJoinContext && b.joinTableAlias != "" {
-	if b.tableAlias != "" && b.tableName != "" {
+		query = addTablePrefix(query, b.joinTableAlias)
-		// Detect if query contains a qualified column reference (e.g., "APIL.column")
+	} else if b.tableAlias != "" && b.tableName != "" {
-		// and replace it with the unqualified version or the correct alias
+		// If we have a table alias defined, check if the query references a different alias
+		// This can happen in preloads where the user expects a certain alias but Bun generates another
 		query = normalizeTableAlias(query, b.tableAlias, b.tableName)
 	}
 	b.query = b.query.Where(query, args...)
 	return b
 }
 
+// addTablePrefix adds a table prefix to unqualified column references
+// This is used in JOIN contexts where conditions must reference the joined table
+func addTablePrefix(query, tableAlias string) string {
+	if tableAlias == "" || query == "" {
+		return query
+	}
+
+	// Split on spaces and parentheses to find column references
+	parts := strings.FieldsFunc(query, func(r rune) bool {
+		return r == ' ' || r == '(' || r == ')' || r == ','
+	})
+
+	modified := query
+	for _, part := range parts {
+		// Check if this looks like an unqualified column reference
+		// (no dot, and likely a column name before an operator)
+		if !strings.Contains(part, ".") {
+			// Extract potential column name (before = or other operators)
+			for _, op := range []string{"=", "!=", "<>", ">", ">=", "<", "<=", " LIKE ", " IN ", " IS "} {
+				if strings.Contains(part, op) {
+					colName := strings.Split(part, op)[0]
+					colName = strings.TrimSpace(colName)
+					if colName != "" && !isOperatorOrKeyword(colName) {
+						// Add table prefix
+						prefixed := tableAlias + "." + colName + strings.TrimPrefix(part, colName)
+						modified = strings.ReplaceAll(modified, part, prefixed)
+						logger.Debug("Adding table prefix '%s' to column '%s' in JOIN condition", tableAlias, colName)
+					}
+					break
+				}
+			}
+		}
+	}
+
+	return modified
+}
+
+// isOperatorOrKeyword checks if a string is likely an operator or SQL keyword
+func isOperatorOrKeyword(s string) bool {
+	s = strings.ToUpper(strings.TrimSpace(s))
+	keywords := []string{"AND", "OR", "NOT", "IN", "IS", "NULL", "TRUE", "FALSE", "LIKE", "BETWEEN"}
+	for _, kw := range keywords {
+		if s == kw {
+			return true
+		}
+	}
+	return false
+}
+
 // normalizeTableAlias replaces table alias prefixes in SQL conditions
 // This handles cases where a user references a table alias that doesn't match
 // what Bun generates (common in preload contexts)
@@ -226,8 +278,8 @@ func normalizeTableAlias(query, expectedAlias, tableName string) string {
 
 			// Check if the prefix matches our expected alias or table name (case-insensitive)
 			if !strings.EqualFold(prefix, expectedAlias) &&
-			   !strings.EqualFold(prefix, tableName) &&
+				!strings.EqualFold(prefix, tableName) &&
-			   !strings.EqualFold(prefix, strings.ToLower(tableName)) {
+				!strings.EqualFold(prefix, strings.ToLower(tableName)) {
 				// This is a different alias - remove the prefix
 				logger.Debug("Stripping incorrect alias '%s' from WHERE condition, keeping just '%s'", prefix, column)
 				// Replace the qualified reference with just the column name
@@ -367,6 +419,27 @@ func (b *BunSelectQuery) Preload(relation string, conditions ...interface{}) com
 // }
 
 func (b *BunSelectQuery) PreloadRelation(relation string, apply ...func(common.SelectQuery) common.SelectQuery) common.SelectQuery {
+	// Auto-detect relationship type and choose optimal loading strategy
+	// Get the model from the query if available
+	model := b.query.GetModel()
+	if model != nil && model.Value() != nil {
+		relType := reflection.GetRelationType(model.Value(), relation)
+
+		// Log the detected relationship type
+		logger.Debug("PreloadRelation '%s' detected as: %s", relation, relType)
+
+		// If this is a belongs-to or has-one relation, use JOIN for better performance
+		if relType.ShouldUseJoin() {
+			logger.Info("Using JOIN strategy for %s relation '%s'", relType, relation)
+			return b.JoinRelation(relation, apply...)
+		}
+
+		// For has-many, many-to-many, or unknown: use separate query (safer default)
+		if relType == reflection.RelationHasMany || relType == reflection.RelationManyToMany {
+			logger.Debug("Using separate query for %s relation '%s'", relType, relation)
+		}
+	}
+
 	// Check if this relation chain would create problematic long aliases
 	relationParts := strings.Split(relation, ".")
 	aliasChain := strings.ToLower(strings.Join(relationParts, "__"))
@@ -473,6 +546,36 @@ func (b *BunSelectQuery) PreloadRelation(relation string, apply ...func(common.S
 	return b
 }
 
+func (b *BunSelectQuery) JoinRelation(relation string, apply ...func(common.SelectQuery) common.SelectQuery) common.SelectQuery {
+	// JoinRelation uses a LEFT JOIN instead of a separate query
+	// This is more efficient for many-to-one or one-to-one relationships
+
+	logger.Debug("JoinRelation '%s' - Using JOIN strategy with automatic WHERE prefix addition", relation)
+
+	// Wrap the apply functions to automatically add table prefix to WHERE conditions
+	wrappedApply := make([]func(common.SelectQuery) common.SelectQuery, 0, len(apply))
+	for _, fn := range apply {
+		if fn != nil {
+			wrappedFn := func(originalFn func(common.SelectQuery) common.SelectQuery) func(common.SelectQuery) common.SelectQuery {
+				return func(q common.SelectQuery) common.SelectQuery {
+					// Create a special wrapper that adds prefixes to WHERE conditions
+					if bunQuery, ok := q.(*BunSelectQuery); ok {
+						// Mark this query as being in JOIN context
+						bunQuery.inJoinContext = true
+						bunQuery.joinTableAlias = strings.ToLower(relation)
+					}
+					return originalFn(q)
+				}
+			}(fn)
+			wrappedApply = append(wrappedApply, wrappedFn)
+		}
+	}
+
+	// Use PreloadRelation with the wrapped functions
+	// Bun's Relation() will use JOIN for belongs-to and has-one relations
+	return b.PreloadRelation(relation, wrappedApply...)
+}
+
 func (b *BunSelectQuery) Order(order string) common.SelectQuery {
 	b.query = b.query.Order(order)
 	return b

pkg/common/adapters/database/gorm.go

@@ -104,10 +104,12 @@ func (g *GormAdapter) RunInTransaction(ctx context.Context, fn func(common.Datab
 
 // GormSelectQuery implements SelectQuery for GORM
 type GormSelectQuery struct {
-	db         *gorm.DB
+	db             *gorm.DB
-	schema     string // Separated schema name
+	schema         string // Separated schema name
-	tableName  string // Just the table name, without schema
+	tableName      string // Just the table name, without schema
-	tableAlias string
+	tableAlias     string
+	inJoinContext  bool   // Track if we're in a JOIN relation context
+	joinTableAlias string // Alias to use for JOIN conditions
 }
 
 func (g *GormSelectQuery) Model(model interface{}) common.SelectQuery {
@@ -151,10 +153,61 @@ func (g *GormSelectQuery) ColumnExpr(query string, args ...interface{}) common.S
 }
 
 func (g *GormSelectQuery) Where(query string, args ...interface{}) common.SelectQuery {
+	// If we're in a JOIN context, add table prefix to unqualified columns
+	if g.inJoinContext && g.joinTableAlias != "" {
+		query = addTablePrefixGorm(query, g.joinTableAlias)
+	}
 	g.db = g.db.Where(query, args...)
 	return g
 }
 
+// addTablePrefixGorm adds a table prefix to unqualified column references (GORM version)
+func addTablePrefixGorm(query, tableAlias string) string {
+	if tableAlias == "" || query == "" {
+		return query
+	}
+
+	// Split on spaces and parentheses to find column references
+	parts := strings.FieldsFunc(query, func(r rune) bool {
+		return r == ' ' || r == '(' || r == ')' || r == ','
+	})
+
+	modified := query
+	for _, part := range parts {
+		// Check if this looks like an unqualified column reference
+		if !strings.Contains(part, ".") {
+			// Extract potential column name (before = or other operators)
+			for _, op := range []string{"=", "!=", "<>", ">", ">=", "<", "<=", " LIKE ", " IN ", " IS "} {
+				if strings.Contains(part, op) {
+					colName := strings.Split(part, op)[0]
+					colName = strings.TrimSpace(colName)
+					if colName != "" && !isOperatorOrKeywordGorm(colName) {
+						// Add table prefix
+						prefixed := tableAlias + "." + colName + strings.TrimPrefix(part, colName)
+						modified = strings.ReplaceAll(modified, part, prefixed)
+						logger.Debug("Adding table prefix '%s' to column '%s' in JOIN condition", tableAlias, colName)
+					}
+					break
+				}
+			}
+		}
+	}
+
+	return modified
+}
+
+// isOperatorOrKeywordGorm checks if a string is likely an operator or SQL keyword (GORM version)
+func isOperatorOrKeywordGorm(s string) bool {
+	s = strings.ToUpper(strings.TrimSpace(s))
+	keywords := []string{"AND", "OR", "NOT", "IN", "IS", "NULL", "TRUE", "FALSE", "LIKE", "BETWEEN"}
+	for _, kw := range keywords {
+		if s == kw {
+			return true
+		}
+	}
+	return false
+}
+
 func (g *GormSelectQuery) WhereOr(query string, args ...interface{}) common.SelectQuery {
 	g.db = g.db.Or(query, args...)
 	return g
@@ -238,6 +291,27 @@ func (g *GormSelectQuery) Preload(relation string, conditions ...interface{}) co
 }
 
 func (g *GormSelectQuery) PreloadRelation(relation string, apply ...func(common.SelectQuery) common.SelectQuery) common.SelectQuery {
+	// Auto-detect relationship type and choose optimal loading strategy
+	// Get the model from GORM's statement if available
+	if g.db.Statement != nil && g.db.Statement.Model != nil {
+		relType := reflection.GetRelationType(g.db.Statement.Model, relation)
+
+		// Log the detected relationship type
+		logger.Debug("PreloadRelation '%s' detected as: %s", relation, relType)
+
+		// If this is a belongs-to or has-one relation, use JOIN for better performance
+		if relType.ShouldUseJoin() {
+			logger.Info("Using JOIN strategy for %s relation '%s'", relType, relation)
+			return g.JoinRelation(relation, apply...)
+		}
+
+		// For has-many, many-to-many, or unknown: use separate query (safer default)
+		if relType == reflection.RelationHasMany || relType == reflection.RelationManyToMany {
+			logger.Debug("Using separate query for %s relation '%s'", relType, relation)
+		}
+	}
+
+	// Use GORM's Preload (separate query strategy)
 	g.db = g.db.Preload(relation, func(db *gorm.DB) *gorm.DB {
 		if len(apply) == 0 {
 			return db
@@ -267,6 +341,42 @@ func (g *GormSelectQuery) PreloadRelation(relation string, apply ...func(common.
 	return g
 }
 
+func (g *GormSelectQuery) JoinRelation(relation string, apply ...func(common.SelectQuery) common.SelectQuery) common.SelectQuery {
+	// JoinRelation uses a JOIN instead of a separate preload query
+	// This is more efficient for many-to-one or one-to-one relationships
+	// as it avoids additional round trips to the database
+
+	// GORM's Joins() method forces a JOIN for the preload
+	logger.Debug("JoinRelation '%s' - Using GORM Joins() with automatic WHERE prefix addition", relation)
+
+	g.db = g.db.Joins(relation, func(db *gorm.DB) *gorm.DB {
+		if len(apply) == 0 {
+			return db
+		}
+
+		wrapper := &GormSelectQuery{
+			db:             db,
+			inJoinContext:  true,                      // Mark as JOIN context
+			joinTableAlias: strings.ToLower(relation), // Use relation name as alias
+		}
+		current := common.SelectQuery(wrapper)
+
+		for _, fn := range apply {
+			if fn != nil {
+				current = fn(current)
+			}
+		}
+
+		if finalGorm, ok := current.(*GormSelectQuery); ok {
+			return finalGorm.db
+		}
+
+		return db
+	})
+
+	return g
+}
+
 func (g *GormSelectQuery) Order(order string) common.SelectQuery {
 	g.db = g.db.Order(order)
 	return g

pkg/common/interfaces.go

@@ -38,6 +38,7 @@ type SelectQuery interface {
 	LeftJoin(query string, args ...interface{}) SelectQuery
 	Preload(relation string, conditions ...interface{}) SelectQuery
 	PreloadRelation(relation string, apply ...func(SelectQuery) SelectQuery) SelectQuery
+	JoinRelation(relation string, apply ...func(SelectQuery) SelectQuery) SelectQuery
 	Order(order string) SelectQuery
 	Limit(n int) SelectQuery
 	Offset(n int) SelectQuery

pkg/common/sql_helpers.go

@@ -1,7 +1,6 @@
 package common
 
 import (
-	"fmt"
 	"strings"
 
 	"github.com/bitechdev/ResolveSpec/pkg/logger"
@@ -9,81 +8,40 @@ import (
 	"github.com/bitechdev/ResolveSpec/pkg/reflection"
 )
 
-// ValidateAndFixPreloadWhere validates that the WHERE clause for a preload contains
+// ValidateAndFixPreloadWhere validates and normalizes WHERE clauses for preloads
-// the relation prefix (alias). If not present, it attempts to add it to column references.
+//
-// Returns the fixed WHERE clause and an error if it cannot be safely fixed.
+// NOTE: For preload queries, table aliases from the parent query are not valid since
+// the preload executes as a separate query with its own table alias. This function
+// now simply validates basic syntax without requiring or adding prefixes.
+// The actual alias normalization happens in the database adapter layer.
+//
+// Returns the WHERE clause and an error if it contains obviously invalid syntax.
 func ValidateAndFixPreloadWhere(where string, relationName string) (string, error) {
 	if where == "" {
 		return where, nil
 	}
 
-	// Check if the relation name is already present in the WHERE clause
+	where = strings.TrimSpace(where)
-	lowerWhere := strings.ToLower(where)
-	lowerRelation := strings.ToLower(relationName)
 
-	// Check for patterns like "relation.", "relation ", or just "relation" followed by a dot
+	// Just do basic validation - don't require or add prefixes
-	if strings.Contains(lowerWhere, lowerRelation+".") ||
+	// The database adapter will handle alias normalization
-		strings.Contains(lowerWhere, "`"+lowerRelation+"`.") ||
+
-		strings.Contains(lowerWhere, "\""+lowerRelation+"\".") {
+	// Check if the WHERE clause contains any qualified column references
-		// Relation prefix is already present
+	// If it does, log a debug message but don't fail - let the adapter handle it
+	if strings.Contains(where, ".") {
+		logger.Debug("Preload WHERE clause for '%s' contains qualified column references: '%s'. "+
+			"Note: In preload context, table aliases from parent query are not available. "+
+			"The database adapter will normalize aliases automatically.", relationName, where)
+	}
+
+	// Validate that it's not empty or just whitespace
+	if where == "" {
 		return where, nil
 	}
 
-	// If the WHERE clause is complex (contains OR, parentheses, subqueries, etc.),
+	// Return the WHERE clause as-is
-	// we can't safely auto-fix it - require explicit prefix
+	// The BunSelectQuery.Where() method will handle alias normalization via normalizeTableAlias()
-	if strings.Contains(lowerWhere, " or ") ||
+	return where, nil
-		strings.Contains(where, "(") ||
-		strings.Contains(where, ")") {
-		return "", fmt.Errorf("preload WHERE condition must reference the relation '%s' (e.g., '%s.column_name'). Complex WHERE clauses with OR/parentheses must explicitly use the relation prefix", relationName, relationName)
-	}
-
-	// Try to add the relation prefix to simple column references
-	// This handles basic cases like "column = value" or "column = value AND other_column = value"
-	// Split by AND to handle multiple conditions (case-insensitive)
-	originalConditions := strings.Split(where, " AND ")
-
-	// If uppercase split didn't work, try lowercase
-	if len(originalConditions) == 1 {
-		originalConditions = strings.Split(where, " and ")
-	}
-
-	fixedConditions := make([]string, 0, len(originalConditions))
-
-	for _, cond := range originalConditions {
-		cond = strings.TrimSpace(cond)
-		if cond == "" {
-			continue
-		}
-
-		// Check if this condition already has a table prefix (contains a dot)
-		if strings.Contains(cond, ".") {
-			fixedConditions = append(fixedConditions, cond)
-			continue
-		}
-
-		// Check if this is a SQL expression/literal that shouldn't be prefixed
-		lowerCond := strings.ToLower(strings.TrimSpace(cond))
-		if IsSQLExpression(lowerCond) {
-			// Don't prefix SQL expressions like "true", "false", "1=1", etc.
-			fixedConditions = append(fixedConditions, cond)
-			continue
-		}
-
-		// Extract the column name (first identifier before operator)
-		columnName := ExtractColumnName(cond)
-		if columnName == "" {
-			// Can't identify column name, require explicit prefix
-			return "", fmt.Errorf("preload WHERE condition must reference the relation '%s' (e.g., '%s.column_name'). Cannot auto-fix condition: %s", relationName, relationName, cond)
-		}
-
-		// Add relation prefix to the column name only
-		fixedCond := strings.Replace(cond, columnName, relationName+"."+columnName, 1)
-		fixedConditions = append(fixedConditions, fixedCond)
-	}
-
-	fixedWhere := strings.Join(fixedConditions, " AND ")
-	logger.Debug("Auto-fixed preload WHERE clause: '%s' -> '%s'", where, fixedWhere)
-	return fixedWhere, nil
 }
 
 // IsSQLExpression checks if a condition is a SQL expression that shouldn't be prefixed

pkg/reflection/model_utils.go

@@ -750,6 +750,118 @@ func ConvertToNumericType(value string, kind reflect.Kind) (interface{}, error)
 	return nil, fmt.Errorf("unsupported numeric type: %v", kind)
 }
 
+// RelationType represents the type of database relationship
+type RelationType string
+
+const (
+	RelationHasMany    RelationType = "has-many"     // 1:N - use separate query
+	RelationBelongsTo  RelationType = "belongs-to"   // N:1 - use JOIN
+	RelationHasOne     RelationType = "has-one"      // 1:1 - use JOIN
+	RelationManyToMany RelationType = "many-to-many" // M:N - use separate query
+	RelationUnknown    RelationType = "unknown"
+)
+
+// ShouldUseJoin returns true if the relation type should use a JOIN instead of separate query
+func (rt RelationType) ShouldUseJoin() bool {
+	return rt == RelationBelongsTo || rt == RelationHasOne
+}
+
+// GetRelationType inspects the model's struct tags to determine the relationship type
+// It checks both Bun and GORM tags to identify the relationship cardinality
+func GetRelationType(model interface{}, fieldName string) RelationType {
+	if model == nil || fieldName == "" {
+		return RelationUnknown
+	}
+
+	modelType := reflect.TypeOf(model)
+	if modelType == nil {
+		return RelationUnknown
+	}
+
+	if modelType.Kind() == reflect.Ptr {
+		modelType = modelType.Elem()
+	}
+
+	if modelType == nil || modelType.Kind() != reflect.Struct {
+		return RelationUnknown
+	}
+
+	// Find the field
+	for i := 0; i < modelType.NumField(); i++ {
+		field := modelType.Field(i)
+
+		// Check if field name matches (case-insensitive)
+		if !strings.EqualFold(field.Name, fieldName) {
+			continue
+		}
+
+		// Check Bun tags first
+		bunTag := field.Tag.Get("bun")
+		if bunTag != "" && strings.Contains(bunTag, "rel:") {
+			// Parse bun relation tag: rel:has-many, rel:belongs-to, rel:has-one, rel:many-to-many
+			parts := strings.Split(bunTag, ",")
+			for _, part := range parts {
+				part = strings.TrimSpace(part)
+				if strings.HasPrefix(part, "rel:") {
+					relType := strings.TrimPrefix(part, "rel:")
+					switch relType {
+					case "has-many":
+						return RelationHasMany
+					case "belongs-to":
+						return RelationBelongsTo
+					case "has-one":
+						return RelationHasOne
+					case "many-to-many", "m2m":
+						return RelationManyToMany
+					}
+				}
+			}
+		}
+
+		// Check GORM tags
+		gormTag := field.Tag.Get("gorm")
+		if gormTag != "" {
+			// GORM uses different patterns:
+			// - foreignKey: usually indicates belongs-to or has-one
+			// - many2many: indicates many-to-many
+			// - Field type (slice vs pointer) helps determine cardinality
+
+			if strings.Contains(gormTag, "many2many:") {
+				return RelationManyToMany
+			}
+
+			// Check field type for cardinality hints
+			fieldType := field.Type
+			if fieldType.Kind() == reflect.Slice {
+				// Slice indicates has-many or many-to-many
+				return RelationHasMany
+			}
+			if fieldType.Kind() == reflect.Ptr {
+				// Pointer to single struct usually indicates belongs-to or has-one
+				// Check if it has foreignKey (belongs-to) or references (has-one)
+				if strings.Contains(gormTag, "foreignKey:") {
+					return RelationBelongsTo
+				}
+				return RelationHasOne
+			}
+		}
+
+		// Fall back to field type inference
+		fieldType := field.Type
+		if fieldType.Kind() == reflect.Slice {
+			// Slice of structs → has-many
+			return RelationHasMany
+		}
+		if fieldType.Kind() == reflect.Ptr || fieldType.Kind() == reflect.Struct {
+			// Single struct → belongs-to (default assumption for safety)
+			// Using belongs-to as default ensures we use JOIN, which is safer
+			return RelationBelongsTo
+		}
+	}
+
+	return RelationUnknown
+}
+
 // GetRelationModel gets the model type for a relation field
 // It searches for the field by name in the following order (case-insensitive):
 // 1. Actual field name