MongoDB: making queries

This is a completed online course called MongoDB: making queries with an estimated workload of 10 hours, carrying out 60 of 60 activities, from 02/27/2024 to 03/01/2024. Topics include the following:

• Preparing the database;
• Find Method;
• Aggregation stages;
• Aggregation operators;
• Other methods.

Preparing the database: after the Showbank2 database creation at NoSQLBooster platform, the command prompt was used in order to make the collections import through the mongoimport command. There are three collections: Accounts (Contas), Clients (Cientes) and Address (Endereco).

Showbank2 database creation

The collections path informed at the command prompt

Import of Accounts collection

Import of Address collection

Import of Clients collection

The imported collections

In order to follow the standard name in plural, the Address (Endereco) collection was renamed as Addresses (Enderecos) collection.

Renamed Addresses collection

Final Showbank2 structure

Find Method: works with many different operators, such as: comparison ($eq, $gt, $gte, $in, $lt, $lte, $ne, $nin), logical ($and, $not, $nor, $or) and array ($all, $elemMatch, $size). Below there are some query operators examples.

Comparison query operator

Logical query operator

Array query operator

Aggregation stages: way of processing a large number of documents in a collection by passing them through different stages that make a pipeline. As the examples below, the stages can filter, sort, group, reshape and modify documents that pass through the pipeline.

$count stage: count documents in a collection

$group stage: groups data based on id

$limit stage: limits the output of documents in a query

$sort stage: sorts the result of a query in ascending (1) or descending (-1) order // $skip stage: controls the initial output of a query’s results

$unwind stage: deconstructs an array field in new documents

$match stage: filters the documents to return in a query

$lookup stage: performs a join between data from two collections

Aggregation operators: used in stages to modify documents and perform calculations. They can work with many different expressions, such as: arithmetic, conditional, date and string.

$rand: returns a random float between 0 and 1

$round: rounds a number to a whole integer or to a specified decimal place

$trunc: truncates a number to a whole integer or to a specified decimal place

$divide: returns the result of dividing the first number by the second. Accepts two argument expressions

$multiply: multiplies numbers to return the product. Accepts any number of argument expressions

$concat: concatenates any number of strings

$split: splits a string into substrings based on a delimiter. Returns an array of substrings

$toLower: converts a string to lowercase. Accepts a single argument expression

$toUpper: converts a string to uppercase. Accepts a single argument expression

$toString: converts value to a string

$year: returns the year for a date as a number

$sum: returns a sum of numerical values // $avg: returns an average of numerical values

$cond: ternary operator that evaluates one expression

$switch: evaluates a series of case expressions

Other methods: in addition to the Find method, there are other methods that can be used to manipulate data stored in MongoDB, such as:

• updateOne: updates a single document within the collection based on the filter;
• updateMany: updates all documents that match the specified filter for a collection;
• findAndModify: updates and returns a single document;
• findOneAndUpdate: updates a single document based on the filter;
• findOneAndReplace: replaces a single document based on the filter;
• findOneAndDelete: deletes a single document based on the filter and sort criteria, returning the deleted document.

In conclusion, the methods, aggregation stages and aggregation operators mentioned above are just part of a large list of options that MongoDB works with.

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[Here is the Certificate of Completion.]