Presented by: Dinesh Chander Abstract: MongoDB has always offered application developers a flexible schema. However, in any organization, a number of factors ranging from risk mitigation to policy may drive the need to enforce a more rigid schema. This feature is a boon to developer productivity, enabling applications to evolve naturally with changing requirements without the need to revisit the schema designs at multiple layers of the stack. In this talk, I will provide an overview of MongoDB's implementation of JSON Schema, an industry standard for data validation. I will also outline how teams can introduce JSON schema validation at just the right time in the lifecycle of their applications, balancing the benefits of developer productivity with requirements for strict schema enforcement.

1. 24TH APRIL, 2018 | BENGALURU
#MDBlocal
Just in Time Validation with
JSON Schema

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Dinesh Chander
Team Lead, Technical Services at
MongoDB
@dineshchandernsit

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Flexible
Schema
Rigid
Schema
Your App

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Flexible
Schema
Rigid
Schema
Your App
risk
success!
regulation
policy
politics
Production
Concerns

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Examples are Here
https://github.com/shannonbradshaw/jsonSchema/blob/m
aster/MongoDB.local.js

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{
_id: 34556,
item: "Flannel T-shirt",
price: NumberDecimal("27.99"),
quantity: NumberInt(1)
color: "green"
}
Simple Schema to Start

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Document Validation (v3.2)
Use query filters to define schema constraints. E.g.,
db.createCollection("orders", {
validator: {
item: {$type: "string"},
price: {$type: "decimal"},
quantity: {$type: "int"},
color: {$in: ["red", "green", "blue"]}
}
});
(ex1 – ex4)

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$jsonSchema

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JSON Schema (v3.6)
● JSON Schema Internet Draft-04 (IETF)
● Is becoming an industry standard
● Widely used; lots of community support
(ex5)

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(ex6 - ex8b)
Let’s make our validator a little
more strict

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Good for Starter Examples
{
_id: 34556,
item: "Flannel T-shirt",
price: NumberDecimal("27.99"),
quantity: NumberLong(1),
color: "green"
}
{
_id: 34556,
total: NumberDecimal("100.00"),
VAT: NumberDecimal("0.20"),
totalWithVAT: NumberDecimal("100.20"),
lineitems: [
{ sku: "MDBTS001",
name: "Flannel T-shirt",
quantity: 2,
unit_price: NumberDecimal(”40.00") },
{ sku: "MDBTS002",
quantity: 4,
unit_price: NumberDecimal(”5.00")}]
}
More Realistic

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Our New Orders Schema
● Orders must contain a lineitems array of 1 to 10 documents
● Documents embedded in lineitems have fields for:
○ sku (required)
○ name (optional)
○ unit_price (required)
○ quantity (required)
● Value of quantity must be an integer
● (Must also contain fields: total, VAT, totalWithVAT, but we'll get to that.)

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Let's validate the line item documents
(embedded in an array)
(ex9 - 10b)

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Now Let's Deal with Totals and VAT
The most recent order we looked at actually contains a few errors:
● The total value should be the sum of each line item sub-total
● I.e., (2 * 40) + (4 * 5) = 100
● The totalWithVAT value should be 100 * 1.002 = 100.2
Can we enforce that totalWithVAT and total are correct using validation?

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Yes we can!
● MongoDB 3.6 -- more expressive query syntax
● Can express complex business rules in validations
● E.g, compute and compare multiple values at runtime

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$expr
Check that totalWithVAT == total * (1+VAT):
$expr: {
$eq: [
"$totalWithVAT",
{$multiply: [
"$total",
{$sum: [1, "$VAT"]}
]}
]
}
Let's add this as a validation rule alongside our JSON Schema validation ()

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Now let's make sure the total is the
sum of the line item subtotals

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Ensure total equals sum of line items
$expr: {
$eq: [
"$total",
{$sum: {
$map: {
"input": "$lineitems",
"as": "item",
"in": {
"$multiply": [
"$$item.quantity",
"$$item.unit_price"
] } } }} ] }

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All together now
(ex11 - 12c)

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Flexible
Schema
Rigid
Schema
Our App

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Flexible
Schema
Rigid
Schema
risk
success!
regulation
policy
politics
Production
Concerns
Our App

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Just the right amount of validation

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When we want it, not before

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Learn More
● Demo - https://github.com/shannonbradshaw/jsonSchema
● MongoDB Documentation
○ Schema Validation -
https://docs.mongodb.com/manual/core/schema-validation/
○ Expressive Query Syntax -
https://www.mongodb.com/blog/post/mongodb-36-json-
schema-validation-expressive-query-syntax
● Free MongoDB 3.6 Online Course from MongoDB University -
https://university.mongodb.com/

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THANK YOU!