import frappe
from frappe.model import no_value_fields
import json

@frappe.whitelist()
def get_preview_data(doctype, docname):
	preview_fields = []
	meta = frappe.get_meta(doctype)
	if not meta.show_preview_popup: return

	preview_fields = [field.fieldname for field in meta.fields \
		if field.in_preview and field.fieldtype not in no_value_fields]

	# no preview fields defined, build list from mandatory fields
	if not preview_fields:
		preview_fields = [field.name for field in meta.fields if field.reqd]

	title_field = meta.get_title_field()
	image_field = meta.image_field

	preview_fields.append(title_field)
	preview_fields.append(image_field)
	preview_fields.append('name')

	preview_data = frappe.get_list(doctype, filters={
		'name': docname
	}, fields=preview_fields, limit=1)

	if not preview_data: return

	preview_data = preview_data[0]

	formatted_preview_data = {
		'preview_image': preview_data.get(image_field),
		'preview_title': preview_data.get(title_field),
		'name': preview_data.get('name'),
	}

	for key, val in preview_data.items():
		if val and meta.has_field(key) and key not in [image_field, title_field, 'name']:
			formatted_preview_data[meta.get_field(key).label] = frappe.format(val, meta.get_field(key).fieldtype)

	return formatted_preview_data
import frappe
from frappe.model import no_value_fields
import json

@frappe.whitelist()
def get_preview_data(doctype, docname):
	preview_fields = []
	meta = frappe.get_meta(doctype)
	if not meta.show_preview_popup: return

	preview_fields = [field.fieldname for field in meta.fields \
		if field.in_preview and field.fieldtype not in no_value_fields]

	# no preview fields defined, build list from mandatory fields
	if not preview_fields:
		preview_fields = [field.fieldname for field in meta.fields if field.reqd]

	title_field = meta.get_title_field()
	image_field = meta.image_field

	preview_fields.append(title_field)
	preview_fields.append(image_field)
	preview_fields.append('name')

	preview_data = frappe.get_list(doctype, filters={
		'name': docname
	}, fields=preview_fields, limit=1)

	if not preview_data: return

	preview_data = preview_data[0]

	formatted_preview_data = {
		'preview_image': preview_data.get(image_field),
		'preview_title': preview_data.get(title_field),
		'name': preview_data.get('name'),
	}

	for key, val in preview_data.items():
		if val and meta.has_field(key) and key not in [image_field, title_field, 'name']:
			formatted_preview_data[meta.get_field(key).label] = frappe.format(val, meta.get_field(key).fieldtype)

	return formatted_preview_data

Use fieldname instead of name for preview_fields (#8184)