modify(SearchConditionStr) 函數用於修改集合中的文件，類似於 SQL 資料庫的 UPDATE 陳述式。它會採用搜尋條件字串 (SearchConditionStr) 作為參數，以指定要修改的文件—關於 SearchConditionStr 的詳細討論，請參閱第 4.3.2 節「Collection.find()」。

如果搜尋條件字串符合一或多個文件，則會使用在 modify() 方法之後鏈結的任何方法來修改它們。它們可以一個接一個地鏈結，並鏈結多次

以下方法可以鏈接到上述的修改方法，以配置修改：

以下是一個使用 sort().limit() 來限制文件修改的範例：

mysql-js> myColl.find("name like '%Doe'");
{
    "_id": "000062b0faf90000000000000001",
    "name": "Jane Doe",
    "favorNum": [
        2,
        3
    ]
}
{
    "_id": "000062b372f80000000000000001",
    "name": "Bob Doe",
    "favorNum": [
        1,
        2
    ]
}
{
    "_id": "000062b372f80000000000000002",
    "name": "Mark Doe",
    "favorNum": [
        7,
        8
    ]
}
{
    "_id": "000062b372f80000000000000003",
    "name": "John Doe",
    "favorNum": [
        0,
        4
    ]
}
mysql-js> myColl.modify("name like '%Doe'").unset("favorNum").sort("name asc").limit(2);
Query OK, 2 items affected (0.0082 sec)

Rows matched: 2  Changed: 2  Warnings: 0
mysql-js> myColl.find("name like '%Doe'").sort('name asc');
{
    "_id": "000062b372f80000000000000001",
    "name": "Bob Doe"
}
{
    "_id": "000062b0faf90000000000000001",
    "name": "Jane Doe"
}
{
    "_id": "000062b372f80000000000000003",
    "name": "John Doe",
    "favorNum": [
        0,
        4
    ]
}
{
    "_id": "000062b372f80000000000000002",
    "name": "Mark Doe",
    "favorNum": [
        7,
        8
    ]
}
4 documents in set (0.0068 sec)

也支援使用 bind() 進行參數綁定。 execute() 函數會觸發 modify() 操作的實際執行。以下範例說明了 modify() 的用法：

// Use the collection 'my_collection'
var myColl = db.getCollection('my_collection');

// Add a new document to the collection 
myColl.add({ name:"John Doe", DOB:"1970-01-01", Phone:1234567, Standing: "Good" }).execute();

// Patch the added document, adding, removing, and changing some fields 
myColl.modify("name = 'John Doe'").patch({ name: "Jane Doe", DOB: null, Phone: 9876543, favorNums: [1,2,3,4,5] }).execute();

//Modify fields with different methods
myColl.modify("name like :param").set("Standing", "Bad").bind("param", "J%Doe").execute();
myColl.modify("name like :param").unset("Phone").bind("param", "J%Doe").execute();
myColl.modify("name like :param").arrayInsert("favorNums[1]", 7).bind("param", "J%Doe").execute();
myColl.modify("name like :param").arrayAppend("favorNums", 99).bind("param", "J%Doe").execute();
myColl.modify("name like :param").unset("favorNums[2]").bind("param", "J%Doe").execute();

var doc = myColl.find('name like :param').limit(1).bind('param', 'J%Doe').execute();

print(doc.fetchOne());
/* The output looks like: 
{
    "Standing": "Bad", 
    "_id": "0000626718c10000000000000002", 
    "favorNums": [
        1, 
        7, 
        3, 
        4, 
        5, 
        99
    ], 
    "name": "Jane Doe"
} */

有關 EBNF 中 add() 的語法，請參閱 CollectionModifyFunction。