Nedb db.update()

db.update(query, update, options, callback)

作用：

根據(jù)update參數(shù)的規(guī)則，更新匹配到query的結(jié)果集。

參數(shù)：

query: 與find和findOne中query參數(shù)的用法一致

update: 指定文檔更改規(guī)則。該參數(shù)可以是一個(gè)新的文檔，也可以是一套修飾符，兩者不能同時(shí)使用。使用修飾符時(shí)，如果需要更改的字段不存在，將會(huì)自動(dòng)創(chuàng)建?？捎玫男揎椃?set(改變字段值), $unset(刪除某一字段), $inc(增加某一字段), $min/$max(改變字段值，傳入值需要小于/大于當(dāng)前值), 還有一些用在數(shù)組上的修飾符，$push, $pop, $addTopSet, $pull, $each, $slice，具體用法如下示例。

options: object類(lèi)型。muti(默認(rèn)false)，是否允許修改多條文檔；upsert(默認(rèn)為false)，如果query沒(méi)有匹配到結(jié)果集，有兩種情況需要考慮，一個(gè)是update是一個(gè)簡(jiǎn)單的對(duì)象(不包含任何修飾符)，另一種情況是帶有修飾符，對(duì)第一種情況會(huì)直接將該文檔插入，對(duì)第二種情況會(huì)將通過(guò)修飾符更改后的文檔插入；

callback(可選): 參數(shù)(err, numAffected, affectedDocuments, upsert)。numAffected：被影響的文檔個(gè)數(shù)；affectedDocuments：更新后的文檔。

注意：_id不能被修改

示例：

// 文檔集
// { _id: 'id1', planet: 'Mars', system: 'solar', inhabited: false }
// { _id: 'id2', planet: 'Earth', system: 'solar', inhabited: true }
// { _id: 'id3', planet: 'Jupiter', system: 'solar', inhabited: false }
// { _id: 'id4', planet: 'Omicron Persia 8', system: 'futurama', inhabited: true }
 
// 用一個(gè)文檔替換另一個(gè)文檔
db.update({ planet: 'Jupiter' }, { planet: 'Pluton'}, {}, function (err, numReplaced) {
  // numReplaced = 1
  // The doc #3 has been replaced by { _id: 'id3', planet: 'Pluton' }
  // Note that the _id is kept unchanged, and the document has been replaced
  // (the 'system' and inhabited fields are not here anymore)
});
 
// 設(shè)定一個(gè)已存字段的值
db.update({ system: 'solar' }, { $set: { system: 'solar system' } }, { multi: true }, function (err, numReplaced) {
  // numReplaced = 3
  // Field 'system' on Mars, Earth, Jupiter now has value 'solar system'
});
 
// 設(shè)定一個(gè)不存在字段的值
db.update({ planet: 'Mars' }, { $set: { "data.satellites": 2, "data.red": true } }, {}, function () {
  // Mars document now is { _id: 'id1', system: 'solar', inhabited: false
  //                      , data: { satellites: 2, red: true }
  //                      }
  // Not that to set fields in subdocuments, you HAVE to use dot-notation
  // Using object-notation will just replace the top-level field
  db.update({ planet: 'Mars' }, { $set: { data: { satellites: 3 } } }, {}, function () {
    // Mars document now is { _id: 'id1', system: 'solar', inhabited: false
    //                      , data: { satellites: 3 }
    //                      }
    // You lost the "data.red" field which is probably not the intended behavior
  });
});
 
// 刪除一個(gè)字段
db.update({ planet: 'Mars' }, { $unset: { planet: true } }, {}, function () {
  // Now the document for Mars doesn't contain the planet field
  // You can unset nested fields with the dot notation of course
});
 
// 設(shè)置upsert
db.update({ planet: 'Pluton' }, { planet: 'Pluton', inhabited: false }, { upsert: true }, function (err, numReplaced, upsert) {
  // numReplaced = 1, upsert = { _id: 'id5', planet: 'Pluton', inhabited: false }
  // A new document { _id: 'id5', planet: 'Pluton', inhabited: false } has been added to the collection
});
 
// If you upsert with a modifier, the upserted doc is the query modified by the modifier
// This is simpler than it sounds :)
db.update({ planet: 'Pluton' }, { $inc: { distance: 38 } }, { upsert: true }, function () {
  // A new document { _id: 'id5', planet: 'Pluton', distance: 38 } has been added to the collection  
});
 
// If we insert a new document { _id: 'id6', fruits: ['apple', 'orange', 'pear'] } in the collection,
// let's see how we can modify the array field atomically
 
// $push inserts new elements at the end of the array
db.update({ _id: 'id6' }, { $push: { fruits: 'banana' } }, {}, function () {
  // Now the fruits array is ['apple', 'orange', 'pear', 'banana']
});
 
// $pop removes an element from the end (if used with 1) or the front (if used with -1) of the array
db.update({ _id: 'id6' }, { $pop: { fruits: 1 } }, {}, function () {
  // Now the fruits array is ['apple', 'orange']
  // With { $pop: { fruits: -1 } }, it would have been ['orange', 'pear']
});
 
// $addToSet adds an element to an array only if it isn't already in it
// Equality is deep-checked (i.e. $addToSet will not insert an object in an array already containing the same object)
// Note that it doesn't check whether the array contained duplicates before or not
db.update({ _id: 'id6' }, { $addToSet: { fruits: 'apple' } }, {}, function () {
  // The fruits array didn't change
  // If we had used a fruit not in the array, e.g. 'banana', it would have been added to the array
});
 
// $pull removes all values matching a value or even any NeDB query from the array
db.update({ _id: 'id6' }, { $pull: { fruits: 'apple' } }, {}, function () {
  // Now the fruits array is ['orange', 'pear']
});
db.update({ _id: 'id6' }, { $pull: { fruits: $in: ['apple', 'pear'] } }, {}, function () {
  // Now the fruits array is ['orange']
});
 
// $each can be used to $push or $addToSet multiple values at once
// This example works the same way with $addToSet
db.update({ _id: 'id6' }, { $push: { fruits: { $each: ['banana', 'orange'] } } }, {}, function () {
  // Now the fruits array is ['apple', 'orange', 'pear', 'banana', 'orange']
});
 
// $slice can be used in cunjunction with $push and $each to limit the size of the resulting array.
// A value of 0 will update the array to an empty array. A positive value n will keep only the n first elements
// A negative value -n will keep only the last n elements.
// If $slice is specified but not $each, $each is set to []
db.update({ _id: 'id6' }, { $push: { fruits: { $each: ['banana'], $slice: 2 } } }, {}, function () {
  // Now the fruits array is ['apple', 'orange']
});
 
// $min/$max to update only if provided value is less/greater than current value
// Let's say the database contains this document
// doc = { _id: 'id', name: 'Name', value: 5 }
db.update({ _id: 'id1' }, { $min: { value: 2 } }, {}, function () {
  // The document will be updated to { _id: 'id', name: 'Name', value: 2 }
});
 
db.update({ _id: 'id1' }, { $min: { value: 8 } }, {}, function () {
  // The document will not be modified
});