MongoDB Query Document

This tutorial will help you to get a clear understanding to use the query operations using the db.collection.find() function.

1. Sample Collection
2. Query Documents
3. Query on Embedded/Nested Documents
4. Query an Array
5. Query an Array of Embedded Documents

Sample Collection

I am going to use the below `books` collection for all the sample query.

db.books.insertMany([
{
    "name" : "The Little Prince",
    "author" : {
            "name" : "Antoine de Saint-Exupery",
            "born" : 1900,
            "died" : 1944,
            "occupation" : ["Aviator", "writer"]
    },
    "language" : ["French"],
    "year":1943,
    "sales": 200,
    "genre": ["fantasy"],
    "rating": [4.5, 5, 4.6, 4.8],
    "sales_year": [
            {year:1950, sales:10000},
            {year:1960, sales:25400},
    ]
},
{
    "name" : "The Lord of the Rings	",
    "author" : {
            "name" : "J. R. R. Tolkien",
            "born" : 1892,
            "died" : 1973,
            "occupation" : ["Author", "Academic", "philologist", "poet"]
    },
    "language" : ["English"],
    "year":1954,
    "sales": 150,
    "genre": ["fantasy"],
    "rating": [4, 3, 3.2],
    "sales_year": [
            {year:1960, sales:15000},
            {year:1970, sales:75220},
    ]
},
{
    "name" : "The Alchemist (O Alquimista)",
    "author" : {
            "name" : "Paulo Coelho",
            "born" : 1947,
            "occupation" : ["lyricist", "writer"]
    },
    "language" : ["English", "Portuguese"],
    "year":1988,
    "sales": 150,
    "genre": ["fantasy"],
    "rating": [5, 4.8, 4.5],
    "sales_year": [
		{year:1990, sales:33600},
		{year:2000, sales:55590},
    ]
},
{
    "name" : "Harry Potter and the Philosopher's Stone",
    "author" : {
            "name" : "J. K. Rowling",
            "born" : 1965,
            "occupation" : ["Author", "philanthropist", "writer"]
    },
    "language" : ["English"],
    "year":1997,
    "sales": 120,
    "genre": ["fantasy", "mystery"],
    "rating": [4.8, 4.5],
    "sales_year": [
            {year:2000, sales:85000},
            {year:2010, sales:95400},
    ]
},
{
    "name" : "The Hobbit",
    "author" : {
            "name" : "J. R. R. Tolkien",
            "born" : 1892,
            "died" : 1973,
            "occupation" : ["Author", "Academic", "philologist", "poet"]
    },
    "language" : ["English"],
    "year":1937,
    "sales": 100,
    "genre": ["fantasy"],
    "rating": [3, 3.5],
    "sales_year": [
            {year:1950, sales:15000},
            {year:1960, sales:66840},
    ]
}
]);
{
        "acknowledged" : true,
        "insertedIds" : [
                ObjectId("5ecd0fa1aa27864f8014d3ee"),
                ObjectId("5ecd0fa1aa27864f8014d3ef"),
                ObjectId("5ecd0fa1aa27864f8014d3f0"),
                ObjectId("5ecd0fa1aa27864f8014d3f1"),
                ObjectId("5ecd0fa1aa27864f8014d3f2")
        ]
}
>

Query Documents:

Using find() function, you can select all the documents from collection.

db.books.find({})

I will share some interesting details here based on mysql query. It will help you to get a great idea about How to use find() in mongo query.

Mongo Query	SQL Query
db.books.find({})	SELECT * FROM books
db.books.find({ sales: 100 })	SELECT * FROM books WHERE sales = 100
db.books.find({language:{$in:["French","Portuguese"]}})	SELECT * FROM books WHERE language IN ("French","Portuguese")
db.books.find( {sales: 150, year:{$gt: 1980}})	SELECT * FROM books WHERE sales = 150 AND year > 1980
db.books.find( { $or: [{sales: 150}, {year:{$gt: 1980}}]})	SELECT * FROM books WHERE sales = 150 OR year > 1980
db.books.find( {language:'Portuguese', $or: [{sales: 150}, {year:{$gt: 1980}}]})	SELECT * FROM books WHERE language = "Portuguese" AND ( sales < 150 OR year > 1980)

Query on Embedded/Nested Documents

{
    "name" : "The Little Prince",
    "author" : {
            "name" : "Antoine de Saint-Exupery",
            "born" : 1900,
            "died" : 1944,
            "occupation" : ["Aviator", "writer"]
    },
    "language" : ["French"],
    "year":1943,
    "sales": 200,
    "genre": ["fantasy"],
    "rating": [4.5, 5, 4.6, 4.8],
    "sales_year": [
            {year:1950, sales:10000},
            {year:1960, sales:25400},
    ]
},

Use { <field>: <value> } condition format for below queries to match the element in the documents

db.books.find( { "author.born":1892 } )

db.books.find( { "author.born":{$gt:1892} } )

db.books.find( { "author.born":{$gt:1892}, "sales":120 } )

db.books.find( { "author.occupation":"Author"});

db.books.find( { "author.occupation":{$in:["Author","writer"]}});

db.books.find( { "author.born":{$gt:1892}, "sales":120, "author.occupation":{$in:["Author","writer"]} )

Query an Array

{
    "name" : "The Alchemist (O Alquimista)",
    "author" : {
            "name" : "Paulo Coelho",
            "born" : 1947,
            "occupation" : ["lyricist", "writer"]
    },
    "language" : ["English", "Portuguese"],
    "year":1988,
    "sales": 150,
    "genre": ["fantasy"],
    "rating": [5, 4.8, 4.5],
    "sales_year": [
		{year:1990, sales:33600},
		{year:2000, sales:55590},
    ]
},

Use { <field>: <value> } condition format for below queries to match the element in the array

Exact match with element count	db.books.find( { language:["English"]} )
* Match element * Exact match not required	db.books.find( { language:{$all:["English"]}} )
Search the string	db.books.find( { language:"English"} )
Condition with operator	db.books.find( { rating: { $gt: 4.9 } } )
Multiple Conditions	db.books.find( { rating: { $gt: 4.9, $lt: 5 } } ) db.books.find( { rating: { $gt: 4.9, $lt: 5 } , language:"English"} )
Multiple Conditions with elemMatch	db.books.find( { rating: { $elemMatch: { $gte: 4.9, $lte: 5 } } } )
Query By Index Position	db.books.find( { "rating.0": { $gte: 4.9 } } ) db.books.find( { "rating.1": { $gte: 4.9 } } )
Query By Array Length	db.books.find( { "rating": { $size: 3 } } )

Hint:

• Multiple Conditions: In this example, This condition can satisfy the one element greater than 4.9 condition and another element can satisfy the less than 5 condition, or a single element can satisfy both condition.
• Multiple Conditions with elemMatch: This condition can satisfy at least one element for both condition.
• Query By Index Position: The field and nested field must be inside quotation marks When you use dot(.) notation.
• Query By Array Length: using the $size operator you can query by number of elements in the array.

Query an Array of Embedded Documents

{
    "name" : "The Little Prince",
    "author" : {
            "name" : "Antoine de Saint-Exupery",
            "born" : 1900,
            "died" : 1944,
            "occupation" : ["Aviator", "writer"]
    },
    "language" : ["French"],
    "year":1943,
    "sales": 200,
    "genre": ["fantasy"],
    "rating": [4.5, 5, 4.6, 4.8],
    "sales_year": [
            {year:1950, sales:10000},
            {year:1960, sales:25400},
    ]
},

Exact match including field order	db.books.find( { "sales_year": { year: 1950, sales: 15000 } } )
Exact with no result	db.books.find( { "sales_year": { sales: 15000, year: 1950 } } )
Condition	db.books.find( { 'sales_year.sales': { $gte: 10000 } } )
Index for a Field	db.books.find( { 'sales_year.0.sales': { $gte: 60000 } } )
elemMatch	db.books.find( { "sales_year": { $elemMatch: { sales: 10000, year: 1950 } } } ) db.books.find( { "sales_year": { $elemMatch: { sales: { $gt: 60000, $lte: 70000 } } } } )
Compound conditions	db.books.find( { "sales_year.sales": { $gt: 20000, $lte: 50000 } } )

Hint:

• Exact Match: While running the match query against the embedded/nested document It requires an exact match of the specified document including the field order and field type.
• Exact with No Result: If you change the element order, you will not get any result.
• Compound Condition: This condition can satisfy the one element greater than 20000 condition and another element can satisfy the less than 50000 condition, or a single element can satisfy both condition.