db.collection.find(
  <query>,           // 查詢條件
  <projection>       // 投影(字段控制)
).<cursor_methods>() // 游標(biāo)方法

// 示例：用戶登錄查詢
const user = db.users.findOne(
  { username: "alice123" },
  { password: 0 } // 排除密碼字段
);

// 范圍查詢
db.products.find({
  price: { $gt: 100, $lte: 500 },
  stock: { $exists: true }
});

// 數(shù)組查詢
db.users.find({
  tags: { $in: ["vip", "premium"] },
  age: { $nin: [18, 19, 20] }
});

// AND/OR/NOT組合
db.orders.find({
  $and: [
    { status: "completed" },
    { $or: [
      { payment: "credit" },
      { amount: { $gt: 1000 } }
    ]},
    { $not: { userType: "trial" } }
  ]
});

db.sales.aggregate([
  { $match: { date: { $gte: new Date("2023-01-01") } } },
  { $project: { product: 1, total: { $multiply: ["$price", "$quantity"] } } },
  { $group: { _id: "$product", totalSales: { $sum: "$total" } } },
  { $sort: { totalSales: -1 } },
  { $limit: 10 }
]);

// 創(chuàng)建復(fù)合索引
db.users.createIndex({ age: 1, status: 1 });

// 覆蓋查詢示例
db.users.find(
  { age: { $gt: 25 }, status: "active" },
  { _id: 0, age: 1, status: 1 }
).explain("executionStats");

// 分頁(yè)函數(shù)
function paginate(collection, query, page = 1, pageSize = 10) {
  const skip = (page - 1) * pageSize;
  return {
    data: collection.find(query).skip(skip).limit(pageSize).toArray(),
    total: collection.countDocuments(query),
    page,
    pageSize
  };
}

// 使用示例
const result = paginate(db.products, { category: "electronics" }, 2);

// 不安全
const query = eval(`({ ${userInput} })`);

// 安全做法
const query = { status: userInputStatus };

// 設(shè)置最大返回文檔大小
db.runCommand({ setParameter: 1, maxBSONSize: 16777216 });

// 查詢時(shí)添加硬限制
db.logs.find().limit(1000);

// 創(chuàng)建文本索引
db.articles.createIndex({ content: "text" });

// 文本搜索查詢
db.articles.find(
  { $text: { $search: "mongodb tutorial" } },
  { score: { $meta: "textScore" } }
).sort({ score: { $meta: "textScore" } });

// 創(chuàng)建2dsphere索引
db.places.createIndex({ location: "2dsphere" });

// 附近地點(diǎn)查詢
db.places.find({
  location: {
    $near: {
      $geometry: {
        type: "Point",
        coordinates: [longitude, latitude]
      },
      $maxDistance: 1000 // 1公里內(nèi)
    }
  }
});

// 獲取查詢執(zhí)行計(jì)劃
const explanation = db.orders
  .find({ status: "shipped", amount: { $gt: 100 } })
  .explain("executionStats");

// 關(guān)鍵指標(biāo)解讀
console.log({
  executionTime: explanation.executionStats.executionTimeMillis,
  totalDocsExamined: explanation.executionStats.totalDocsExamined,
  indexUsed: explanation.executionStats.executionStages.inputStage.indexName
});