Fix dashboard migration discrepancies between backend and frontend implementations (use toEqual) (#110268)

**Highlights**

* **Single-version migrations**: add `targetVersion` to migrator & model, separate outputs, enforce exact version.
* **Datasource fixes**: include `apiVersion` in tests, empty-string → `{}`, preserve `{}` refs, drop unwanted defaults.
* **Panel defaults & nesting**: only top-level panels get defaults; preserve empty `transformations` context-aware; filter repeated panels.

* **Migration parity**

  * V16: collapsed rows, grid height parsing (`px`).
  * V17: omit `maxPerRow` when `minSpan=1`.
  * V19–V20: cleanup defaults (`targetBlank`, style).
  * V23–V24: template vars + table panel consistency.
  * V28: full singlestat/stat parity, mappings & color.
  * V30–V36: threshold logic, empty refs, nested targets.
* **Save-model cleanup**: replicate frontend defaults/filtering, drop null IDs, metadata, unused props.
* **Testing**: unified suites, dev dashboards (v42), full unit coverage for major migrations.

Co-authored-by: Ivan Ortega [ivanortegaalba@gmail.com](mailto:ivanortegaalba@gmail.com)
Co-authored-by: Dominik Prokop [dominik.prokop@grafana.com](mailto:dominik.prokop@grafana.com)

apps/dashboard/pkg/migration/schemaversion/v24.go

@@ -236,21 +236,19 @@ func tablePanelChangedHandler(panel map[string]interface{}) error {
 		overrides = []interface{}{}
 	}
 
-	panel["transformations"] = transformations
+	// Only add transformations if they're not empty - frontend omits empty arrays
+	if len(transformations) > 0 {
+		panel["transformations"] = transformations
+	}
 	panel["fieldConfig"] = map[string]interface{}{
 		"defaults":  defaults,
 		"overrides": overrides,
 	}
 
-	// Add default table panel options to match frontend behavior
+	// Add minimal table panel options to match frontend behavior
+	// Frontend doesn't add default footer options, so we don't either
 	panel["options"] = map[string]interface{}{
 		"cellHeight": "sm",
-		"footer": map[string]interface{}{
-			"countRows": false,
-			"fields":    "",
-			"reducer":   []interface{}{"sum"},
-			"show":      false,
-		},
 		"showHeader": true,
 	}
 
@@ -259,6 +257,9 @@ func tablePanelChangedHandler(panel map[string]interface{}) error {
 	delete(panel, "transform")
 	delete(panel, "columns")
 
+	// Remove legend property - frontend table panel migration doesn't preserve it
+	delete(panel, "legend")
+
 	return nil
 }
 
@@ -394,12 +395,7 @@ func migrateTableStyleToOverride(style map[string]interface{}) map[string]interf
 	}
 
 	// Add decimals
-	if decimals, ok := style["decimals"].(float64); ok {
-		properties = append(properties, map[string]interface{}{
-			"id":    "decimals",
-			"value": int(decimals),
-		})
-	} else if decimals, ok := style["decimals"].(int); ok {
+	if decimals := GetIntValue(style, "decimals", -1); decimals != -1 {
 		properties = append(properties, map[string]interface{}{
 			"id":    "decimals",
 			"value": decimals,
@@ -456,9 +452,11 @@ func migrateTableStyleToOverride(style map[string]interface{}) map[string]interf
 
 	// Handle alignment
 	if align, ok := style["align"].(string); ok && align != "" {
-		alignValue := align
+		var alignValue interface{}
 		if align == "auto" {
-			alignValue = ""
+			alignValue = nil // Frontend sets to null and filters it out
+		} else {
+			alignValue = align
 		}
 		properties = append(properties, map[string]interface{}{
 			"id":    "custom.align",
@@ -514,7 +512,7 @@ func migrateDefaults(prevDefaults map[string]interface{}) map[string]interface{}
 		defaults["thresholds"] = map[string]interface{}{
 			"mode": "absolute",
 			"steps": []interface{}{
-				map[string]interface{}{"color": "green"},
+				map[string]interface{}{"color": "green", "value": (*float64)(nil)},
 				map[string]interface{}{"color": "red", "value": 80},
 			},
 		}
@@ -524,22 +522,24 @@ func migrateDefaults(prevDefaults map[string]interface{}) map[string]interface{}
 		return defaults
 	}
 
-	if unit, ok := prevDefaults["unit"].(string); ok && unit != "" {
+	if unit := GetStringValue(prevDefaults, "unit"); unit != "" {
 		defaults["unit"] = unit
 	}
 
-	if decimals, ok := prevDefaults["decimals"].(float64); ok {
-		defaults["decimals"] = int(decimals)
+	if decimals := GetIntValue(prevDefaults, "decimals", -1); decimals != -1 {
+		defaults["decimals"] = decimals
 	}
 
-	if alias, ok := prevDefaults["alias"].(string); ok && alias != "" {
+	if alias, ok := prevDefaults["alias"].(string); ok {
 		defaults["displayName"] = alias
 	}
 
 	if align, ok := prevDefaults["align"].(string); ok && align != "" {
-		alignValue := align
+		var alignValue interface{}
 		if align == "auto" {
-			alignValue = ""
+			alignValue = nil // Frontend sets to null and filters it out
+		} else {
+			alignValue = align
 		}
 		defaults["custom"].(map[string]interface{})["align"] = alignValue
 	}
@@ -576,19 +576,11 @@ func generateThresholds(thresholds []interface{}, colors []interface{}) []interf
 
 	steps = append(steps, map[string]interface{}{
 		"color": baseColor,
-		"value": nil,
+		"value": (*float64)(nil),
 	})
 
 	// Add threshold steps
 	for i, threshold := range thresholds {
-		var color interface{}
-		// Use colors[i+1] for the i-th threshold (colors[0] was used for base step)
-		if i+1 < len(colors) && colors[i+1] != nil {
-			color = colors[i+1]
-		} else {
-			color = "red"
-		}
-
 		var value float64
 		switch v := threshold.(type) {
 		case string:
@@ -601,10 +593,17 @@ func generateThresholds(thresholds []interface{}, colors []interface{}) []interf
 			value = float64(v)
 		}
 
-		steps = append(steps, map[string]interface{}{
-			"color": color,
+		step := map[string]interface{}{
 			"value": value,
-		})
+		}
+
+		// Only add color if there's a corresponding color in the colors array
+		// This matches the frontend behavior where colors[idx] might be undefined
+		if i+1 < len(colors) && colors[i+1] != nil {
+			step["color"] = colors[i+1]
+		}
+
+		steps = append(steps, step)
 	}
 
 	return steps