$ifNull
The $ifNull operator is used to evaluate an expression and return a specified value if the expression resolves to null.
$ifNull
The $ifNull operator is used to evaluate an expression and return a specified value if the expression resolves to null. This operator is useful in scenarios where you want to provide a default value for fields that may not exist or may have null values.
Syntax
{
$ifNull: [ <expression>, <replacement-value> ]
}Parameters
| Parameter | Description |
|---|---|
<expression> | The expression to evaluate. |
<replacement-value> | The value to return if the expression evaluates to null |
Examples
Consider this sample document from the stores collection.
{
"_id": "0fcc0bf0-ed18-4ab8-b558-9848e18058f4",
"name": "First Up Consultants | Beverage Shop - Satterfieldmouth",
"location": {
"lat": -89.2384,
"lon": -46.4012
},
"staff": {
"totalStaff": {
"fullTime": 8,
"partTime": 20
}
},
"sales": {
"totalSales": 75670,
"salesByCategory": [
{
"categoryName": "Wine Accessories",
"totalSales": 34440
},
{
"categoryName": "Bitters",
"totalSales": 39496
},
{
"categoryName": "Rum",
"totalSales": 1734
}
]
},
"promotionEvents": [
{
"eventName": "Unbeatable Bargain Bash",
"promotionalDates": {
"startDate": {
"Year": 2024,
"Month": 6,
"Day": 23
},
"endDate": {
"Year": 2024,
"Month": 7,
"Day": 2
}
},
"discounts": [
{
"categoryName": "Whiskey",
"discountPercentage": 7
},
{
"categoryName": "Bitters",
"discountPercentage": 15
},
{
"categoryName": "Brandy",
"discountPercentage": 8
},
{
"categoryName": "Sports Drinks",
"discountPercentage": 22
},
{
"categoryName": "Vodka",
"discountPercentage": 19
}
]
},
{
"eventName": "Steal of a Deal Days",
"promotionalDates": {
"startDate": {
"Year": 2024,
"Month": 9,
"Day": 21
},
"endDate": {
"Year": 2024,
"Month": 9,
"Day": 29
}
},
"discounts": [
{
"categoryName": "Organic Wine",
"discountPercentage": 19
},
{
"categoryName": "White Wine",
"discountPercentage": 20
},
{
"categoryName": "Sparkling Wine",
"discountPercentage": 19
},
{
"categoryName": "Whiskey",
"discountPercentage": 17
},
{
"categoryName": "Vodka",
"discountPercentage": 23
}
]
}
]
}Example 1: Default value for missing store.manager field
To ensure that the $staff.totalStaff.intern field is always a number, you can use $ifNull to replace null values with 0.
db.stores.aggregate([
{
$project: {
name: 1,
interns: { $ifNull: ["$staff.totalStaff.intern", 0] }
}
},
// Limit the result to the first 3 documents
{ $limit: 3 }
])The first three results returned by this query are:
[
{
"_id": "7954bd5c-9ac2-4c10-bb7a-2b79bd0963c5",
"name": "Lakeshore Retail | DJ Equipment Stop - Port Cecile",
"interns": 0
},
{
"_id": "649626c9-eda1-46c0-a27f-dcee19d97f41",
"name": "VanArsdel, Ltd. | Musical Instrument Outlet - East Cassie",
"interns": 0
},
{
"_id": "8345de34-73ec-4a99-9cb6-a81f7b145c34",
"name": "Northwind Traders | Bed and Bath Place - West Oraland",
"interns": 0
}
]