diff --git a/dist/js/bundle.js b/dist/js/bundle.js
index ca0796b1..71692006 100644
--- a/dist/js/bundle.js
+++ b/dist/js/bundle.js
@@ -1240,14 +1240,14 @@ var router = class Router {
 };
 
 var observable = class Observable {
-	constructor() {
-		this._handlers = {};
-	}
+    constructor() {
+        this._handlers = {};
+    }
 
     on(event, fn) {
         if (!this._handlers[event]) {
-			this._handlers[event] = [];
-		}
+            this._handlers[event] = [];
+        }
         this._handlers[event].push(fn);
     }
 
@@ -2741,6 +2741,7 @@ var account_client = {
     List: AccountList
 };
 
+// start server
 client.start({
     server: 'localhost:8000',
     container: document.querySelector('.wrapper'),
diff --git a/models/doctype/account/account.json b/models/doctype/account/account.json
index ecad766b..cb8a86fe 100644
--- a/models/doctype/account/account.json
+++ b/models/doctype/account/account.json
@@ -1,7 +1,7 @@
 {
 	"name": "Account",
 	"doctype": "DocType",
-	"issingle": 0,
+	"is_single": 0,
 	"keyword_fields": [
 		"name",
 		"account_type"
@@ -17,7 +17,7 @@
 			"fieldname": "parent_account",
 			"label": "Parent Account",
 			"fieldtype": "Link",
-			"options": "Account"
+			"target": "Account"
 		},
 		{
 			"fieldname": "account_type",
diff --git a/models/doctype/customer/customer.json b/models/doctype/customer/customer.json
index 2c6f09e2..f1e68fd9 100644
--- a/models/doctype/customer/customer.json
+++ b/models/doctype/customer/customer.json
@@ -1,7 +1,7 @@
 {
 	"name": "Customer",
 	"doctype": "DocType",
-	"issingle": 0,
+	"is_single": 0,
 	"istable": 0,
 	"keyword_fields": [
 		"name"
diff --git a/models/doctype/invoice/invoice.js b/models/doctype/invoice/invoice.js
new file mode 100644
index 00000000..951a747f
--- /dev/null
+++ b/models/doctype/invoice/invoice.js
@@ -0,0 +1,27 @@
+const BaseMeta = require('frappejs/model/meta');
+const BaseDocument = require('frappejs/model/document');
+
+class InvoiceMeta extends BaseMeta {
+	setup_meta() {
+		Object.assign(this, require('./invoice.json'));
+	}
+}
+
+class Invoice extends BaseDocument {
+	setup() {
+		this.add_handler('validate');
+	}
+
+	validate() {
+		this.total = this.get_total();
+	}
+
+	get_total() {
+		return this.items.map(d => d.amount).reduce((a, b) => a + b, 0);
+	}
+}
+
+module.exports = {
+	Document: Invoice,
+	Meta: InvoiceMeta
+};
\ No newline at end of file
diff --git a/models/doctype/invoice/invoice.json b/models/doctype/invoice/invoice.json
new file mode 100644
index 00000000..2ec20ab9
--- /dev/null
+++ b/models/doctype/invoice/invoice.json
@@ -0,0 +1,30 @@
+{
+	"name": "Invoice",
+	"doctype": "DocType",
+	"is_single": 0,
+	"istable": 0,
+	"keyword_fields": [],
+	"fields": [
+		{
+			"fieldname": "customer",
+			"label": "Customer",
+			"fieldtype": "Link",
+			"target": "Customer",
+			"reqd": 1
+		},
+		{
+			"fieldname": "items",
+			"label": "Items",
+			"fieldtype": "Table",
+			"childtype": "Invoice Item",
+			"reqd": 1
+		},
+		{
+			"fieldname": "total",
+			"label": "Total",
+			"fieldtype": "Currency",
+			"formula": "doc.get_total()",
+			"reqd": 1
+		}
+	]
+}
\ No newline at end of file
diff --git a/models/doctype/invoice_item/invoice_item.js b/models/doctype/invoice_item/invoice_item.js
new file mode 100644
index 00000000..62fb348b
--- /dev/null
+++ b/models/doctype/invoice_item/invoice_item.js
@@ -0,0 +1,16 @@
+const BaseMeta = require('frappejs/model/meta');
+const BaseDocument = require('frappejs/model/document');
+
+class InvoiceItemMeta extends BaseMeta {
+	setup_meta() {
+		Object.assign(this, require('./invoice_item.json'));
+	}
+}
+
+class InvoiceItem extends BaseDocument {
+}
+
+module.exports = {
+	Document: InvoiceItem,
+	Meta: InvoiceItemMeta
+};
\ No newline at end of file
diff --git a/models/doctype/invoice_item/invoice_item.json b/models/doctype/invoice_item/invoice_item.json
new file mode 100644
index 00000000..3ec56fc7
--- /dev/null
+++ b/models/doctype/invoice_item/invoice_item.json
@@ -0,0 +1,42 @@
+{
+	"name": "Invoice Item",
+	"doctype": "DocType",
+	"is_single": 0,
+	"is_child": 1,
+	"keyword_fields": [],
+	"fields": [
+		{
+			"fieldname": "item",
+			"label": "Item",
+			"fieldtype": "Link",
+			"options": "Item",
+			"reqd": 1
+		},
+		{
+			"fieldname": "description",
+			"label": "Description",
+			"fieldtype": "Text",
+			"fetch": "item.description",
+			"reqd": 1
+		},
+		{
+			"fieldname": "quantity",
+			"label": "Quantity",
+			"fieldtype": "Float",
+			"reqd": 1
+		},
+		{
+			"fieldname": "rate",
+			"label": "Rate",
+			"fieldtype": "Currency",
+			"reqd": 1
+		},
+		{
+			"fieldname": "amount",
+			"label": "Amount",
+			"fieldtype": "Currency",
+			"readonly": 1,
+			"formula": "doc.quantity * doc.rate"
+		}
+	]
+}
\ No newline at end of file
diff --git a/models/doctype/item/item.json b/models/doctype/item/item.json
index 36100b79..11329750 100644
--- a/models/doctype/item/item.json
+++ b/models/doctype/item/item.json
@@ -1,7 +1,7 @@
 {
 	"name": "Item",
 	"doctype": "DocType",
-	"issingle": 0,
+	"is_single": 0,
 	"keyword_fields": [
 		"name",
 		"description"