Atualizações posicionais e posicionais filtradas
Você atualizará no próprio lugar os elementos correspondentes de uma matriz usando o operador posicional $ e o operador posicional filtrado $[identifier].
Atualizações posicionais e posicionais filtradas é uma aula grátis de MongoDB Academy no CoddyKit. Esta é a aula 4 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de MongoDB Academy, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de MongoDB Academy inclui 4 aulas no total.
Partes desta aula ainda não foram traduzidas e aparecem em inglês.
Updating Elements Inside Arrays
While $push and $pull add and remove array elements, sometimes you need to modify an existing element in place—change a field inside a sub-document that is already in the array. MongoDB provides two positional operators for this: the $ positional operator for updating the first matching element, and the $[identifier] filtered positional operator for updating all matching elements.
The $ Positional Operator
The $ positional operator acts as a placeholder for the index of the first array element that matched the query filter. You use it in the update's field path like 'arrayField.$.subField', and MongoDB replaces $ with the index of the matched element. The query filter must include a condition on the array field so MongoDB knows which element to target.
// Update the grade of the first matching scores element
db.students.updateOne(
{
_id: studentId,
'scores.subject': 'math' // match condition identifies which element
},
{
$set: { 'scores.$.grade': 'A+' } // $ = index of matched element
}
);
// Only the FIRST element where subject='math' is updatedLimitations of the $ Operator
The $ positional operator has two important limitations: it only updates the first matching element (not all matching elements), and it cannot be used with updateMany() to safely update specific array elements across multiple documents (it updates the first match per document). For updating all matching elements or multiple documents, you need the filtered positional operator.
// Document: { scores: [{ subject: 'math', pass: false }, { subject: 'math', pass: false }] }
// $ only updates the FIRST math element
db.students.updateOne(
{ _id: id, 'scores.subject': 'math' },
{ $set: { 'scores.$.pass': true } }
);
// Result: [{ subject: 'math', pass: TRUE }, { subject: 'math', pass: FALSE }]
// Second element unchanged!The $[] All Positional Operator
The $[] (all positional) operator updates all elements in an array without needing a filter condition. It acts as a placeholder for every element in the array. Use it when you want to apply the same update to every element of an array field—for example, resetting all flags in a status array or incrementing every score by a bonus amount.
// Give every score a +5 bonus
db.students.updateOne(
{ _id: studentId },
{ $inc: { 'scores.$[].value': 5 } } // applies to ALL elements
);
// Set pass=true for every element in the array
db.students.updateMany(
{},
{ $set: { 'scores.$[].reviewed': true } } // updates across all documents
);The $[identifier] Filtered Positional Operator
The $[identifier] filtered positional operator updates all array elements that match a condition specified in an arrayFilters option. The identifier is a placeholder name you choose (like elem or score), and the arrayFilters option defines which elements the placeholder should target. This gives you precise control over which elements get updated.
// Update ALL math scores (not just the first)
db.students.updateOne(
{ _id: studentId },
{
$set: { 'scores.$[elem].grade': 'A' } // 'elem' is the identifier
},
{
arrayFilters: [{ 'elem.subject': 'math' }] // filter for 'elem'
}
);
// All elements where subject='math' get grade='A'Complex arrayFilters Conditions
The arrayFilters conditions support all standard MongoDB query operators: $gt, $lt, $in, $and, and more. You can define multiple identifiers for nested array updates by using multiple filter objects in the array. Each identifier must be a unique alphanumeric name starting with a lowercase letter.
// Fail all scores below 60 for a student
db.students.updateOne(
{ _id: studentId },
{ $set: { 'scores.$[lowScore].pass': false } },
{ arrayFilters: [{ 'lowScore.value': { $lt: 60 } }] }
);
// Update scores that are math AND below 70
db.students.updateOne(
{ _id: studentId },
{ $set: { 'scores.$[elem].needsHelp': true } },
{
arrayFilters: [{
'elem.subject': 'math',
'elem.value': { $lt: 70 }
}]
}
);Filtered Positional With updateMany
Unlike the $ operator, $[identifier] works safely with updateMany() to apply filtered array updates across all documents in a collection. This makes it extremely powerful for bulk operations like price adjustments on specific product categories embedded in order line items, or applying a discount to certain invoice entries across all users.
// Apply 10% discount to all 'sale' items across ALL orders
db.orders.updateMany(
{}, // all documents
{ $mul: { 'lineItems.$[item].price': 0.9 } },
{ arrayFilters: [{ 'item.category': 'sale' }] }
);
// Mark all pending tasks as 'overdue' if dueDate has passed
db.projects.updateMany(
{},
{ $set: { 'tasks.$[t].status': 'overdue' } },
{ arrayFilters: [{ 't.status': 'pending', 't.dueDate': { $lt: new Date() } }] }
);Nested Array Updates With Multiple Identifiers
For arrays nested inside arrays, you can use multiple identifiers in arrayFilters to target elements at different nesting levels. This is an advanced pattern—each identifier applies to a different depth in the nesting. Be mindful that deeply nested array updates are complex and may indicate a schema that could be restructured for clarity.
// Document: { courses: [{ name: 'Math', lessons: [{ id: 1, done: false }] }] }
// Mark a specific lesson as done inside a specific course
db.students.updateOne(
{ _id: studentId },
{ $set: { 'courses.$[course].lessons.$[lesson].done': true } },
{
arrayFilters: [
{ 'course.name': 'Math' }, // outer array filter
{ 'lesson.id': 1 } // inner array filter
]
}
);Updating by Index With Dot Notation
When you know the exact numeric index of the element you want to update, you can use dot notation directly: 'array.2.field' updates the third element (0-indexed). This is the most direct approach when the position is known at write time. It's commonly used for fixed-position arrays where each index has a defined meaning.
// Update the third element (index 2) directly
db.results.updateOne(
{ _id: testId },
{ $set: { 'answers.2.correct': true } } // update answer at index 2
);
// Set a specific round's score in a game
db.games.updateOne(
{ _id: gameId },
{ $set: { 'rounds.0.score': 150 } } // update round 1 (index 0)
);Combining Positional Operators With Other Updates
Positional operators can be combined with any update operator—$set, $inc, $unset, $push—to perform complex in-place array element modifications in a single atomic operation. For example, incrementing a nested field inside a matching array element while also updating a document-level timestamp.
// Increment attempt count for a specific question in a quiz
db.quizzes.updateOne(
{ _id: quizId, 'questions.id': 'q1' },
{
$inc: { 'questions.$.attemptCount': 1 },
$set: { 'questions.$.lastAttempted': new Date(), updatedAt: new Date() }
}
);
// All changes are atomicWhen to Redesign vs Use Positional Operators
Positional updates are powerful, but complex nested positional patterns can be a sign that your schema needs rethinking. Consider restructuring when: you need to query and update elements from multiple nested arrays frequently; you find yourself writing long dot-notation paths; or your application logic must determine exact element indices at runtime. Often, moving nested data to a separate collection with references is simpler and more maintainable.
// Schema smells that suggest restructuring:
// 'courses.$[c].lessons.$[l].quizzes.$[q].answers.$.correct'
// -> 5 levels of nesting is too complex
// Alternative: separate collections with references
// answers collection: { _id, quizId, lessonId, questionIndex, correct }Quick Check
Test your understanding of positional and filtered positional update operators.
Lesson Recap
In this lesson you learned: $ updates the first matched array element identified by the query filter, $[] updates all array elements unconditionally, and $[identifier] with arrayFilters updates all elements matching a condition. Next up we explore the aggregation pipeline—MongoDB's powerful server-side data transformation engine.
Perguntas Frequentes
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Sim — o texto completo de “Atualizações posicionais e posicionais filtradas” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de MongoDB Academy, atualize para CoddyKit PRO. O curso de MongoDB Academy inclui 4 aulas no total.
O que vou aprender em “Atualizações posicionais e posicionais filtradas”?
Você atualizará no próprio lugar os elementos correspondentes de uma matriz usando o operador posicional $ e o operador posicional filtrado $[identifier]. Você pratica MongoDB Academy com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.
Preciso ter experiência prévia para começar MongoDB Academy?
Nenhuma experiência prévia é necessária. MongoDB Academy no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 4 de 4.
Quanto tempo leva a aula “Atualizações posicionais e posicionais filtradas”?
A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.
Posso escrever e executar código nesta aula de MongoDB Academy?
Sim. Cada aula de MongoDB Academy inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.
Todas as aulas deste curso
- Consultando matrizes: $all, $size e correspondência de elementos
- $elemMatch: correspondendo a subdocumentos de matrizes
- Atualizando matrizes: $push, $pull, $pop, $addToSet
- Atualizações posicionais e posicionais filtradas