MongoDB Mongoose Use Lookup Guide

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In This Blog We Will See Complete Guide For Using Joins With Lookup in Mongoose


Mongoose - Education Funda
MongoDB Mongoose - Education Funda


Simply in MongoDB Mongoose we can use Aggregate Query with $lookup to get data basis upon JOINS. such as below:

await MainModel.aggregate([
{
$match:
{ "COLUMN_NAME": value }
},

{
$lookup:
{
from: 'relation_collection_name',
localField: 'relation_collection_primary_key',
foreignField: 'this_table_foreign_key',
as: 'ALIASING'
}
}
]);

With above query new column added with ALIASING in which relation collection data will also come.

To get data in Object format instead of Array we can use $unwind like below:

await MainModel.aggregate([
{
$match:
{ "COLUMN_NAME": value }
},

{
$lookup:
{
from: 'relation_collection_name',
localField: 'relation_collection_primary_key',
foreignField: 'this_table_foreign_key',
as: 'ALIASING'
}
},

{
$unwind: '$ALIASING'
},
]);

With. above query via using $unwind the data coming in object format now instead of array.

Now, if you want data if no data available in relation table so we can use preserveNullAndEmptyArrays like below:

await MainModel.aggregate([
{
$match:
{ "COLUMN_NAME": value }
},

{
$lookup:
{
from: 'relation_collection_name',
localField: 'relation_collection_primary_key',
foreignField: 'this_table_foreign_key',
as: 'ALIASING'
}
},

{
$unwind: {
path: "$ALIASING",
preserveNullAndEmptyArrays: true
}
},
]);


Now, if you want to use multiple lookup so you can use very simple like below:

await MainModel.aggregate([
{
$match:
{ "COLUMN_NAME": value }
},

{
$lookup:
{
from: 'relation_collection_name',
localField: 'relation_collection_primary_key',
foreignField: 'this_table_foreign_key',
as: 'ALIASING'
}
},

{
$unwind: {
path: "$ALIASING",
preserveNullAndEmptyArrays: true
}
},

{
$lookup:
{
from: 'relation_collection_name_another',
localField: 'relation_collection_primary_key',
foreignField: 'this_table_foreign_key',
as: 'ALIASING_1'
}
},

{
$unwind: {
path: "$ALIASING_1",
preserveNullAndEmptyArrays: true
}
},
]);


Thanks for reading this blog, I hope it will help you to understand Mongoose $Lookup.

Happy Coding !!

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Location: India

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