mongoose 之 population 关联查询

本文分享如何通过 mongoose 的 population 实现关联表查询, population 的 api 可参考这里。
本文demo源码.
1.初始化两个schema和model。

/**
 *  department schema
 **/
var departmentSchema = new Schema({
    id: String, //部门编号
    name: String //名称
});


/**
 *  employee schema
 **/
var employeeSchema = new Schema({
    id: Number, //工号
    name: String, //姓名
    sex: Number, //性别
    age: Number, //年龄
    dep: {
        type: Schema.Types.ObjectId,
        ref: 'department'
    }
});

/**
 *  model
 **/
var employee = mongodb.mongoose.model("employee", employeeSchema);
var department = mongodb.mongoose.model('department', departmentSchema);

employee 的属性 dep，对应model department. ref 表示关联 department model.
被关联的 model 的 type 必须是 ObjectId, Number, String, 和 Buffer.
2.初始化数据。

 //部门表
 db.departments.insert({"id":"1001","name":"市场部"});
 db.departments.insert({"id":"1002","name":"销售部"});
 db.departments.insert({"id":"1003","name":"行政部"});

 //职工表
 db.employees.insert({"id":"001","name":"jack","sex":1,"age":23,"dep":"593667c4ec59b38aefdc25b5"});
 db.employees.insert({"id":"002","name":"tom","sex":2,"age":23,"dep":"593667c4ec59b38aefdc25b6"});
 db.employees.insert({"id":"003","name":"kan","sex":1,"age":43,"dep":"593667c4ec59b38aefdc25b5"});
 db.employees.insert({"id":"004","name":"julis","sex":2,"age":23,"dep":"593667c4ec59b38aefdc25b7"});
 db.employees.insert({"id":"005","name":"michael","sex":1,"age":43,"dep":"593667c4ec59b38aefdc25b5"});
 db.employees.insert({"id":"006","name":"jordan","sex":1,"age":25,"dep":"593667c4ec59b38aefdc25b5"});

注意此处的数据初始化顺序。必须先初始化部门表，然后初始化员工表。
3.使用population关联查询

 employee.find({})    //查询所有的employees表中的数据，并将结果返回给populate
         .populate({ path: 'dep', select: { name: 1 } })   //上述结果集合中的dep字段用departments表中的name字段填充
         .exec(function(err, obj) {
             callback(err, obj);
         });

3.查询结果展示

渲染模版（ejs语法）及渲染语句：

res.render('list', { employeeList: obj });//obj为第三部中查询结果

                    <% for(var i=0; i  
                        
                    <% } %>  
                

                

                    

                        
职工ID
                        
姓名
                        
性别
                        
年龄
                        
部门
                    
                
                

                            
<%= employeeList[i]._doc.id %>
                            
<%= employeeList[i]._doc.name %>
                            

                            <% if(employeeList[i]._doc.sex == 1) { %>
                                男
                            <% } else { %>
                                女
                            <% } %>
                            
                            
<%= employeeList[i]._doc.age %>
                            
<%= employeeList[i]._doc.dep.name %>