如何创建对象数组-Go？

Question

I am working in Go and MongoDB and having the following MongoDB schema

[   
  {
    "name":"sample",
    "time": "2014-04-05",
    "Qty":3
  },
  {
   "name":"sample",
   "time": "2014-04-05",
   "Qty":3
  }
]

I had tried using the following code to create the above document

elements := make([3]map[string]string)
elements["name"] = "karthick"
elements["date"] = "2014-04-05"
elements["qty"] = 3

fmt.Println(elements)

But it is not working.

Error : cannot make type [3]map[string]string

Any suggestion will be grateful

Answer 1

There's a difference between arrays and slices. Arrays are compile time objects while slices are runtime objects. Arrays therefore have more information to offer to the compiler than slices (e.g. length).

In your code, you attempt to create an array of map[string]string with 3 elements. You can do this like this:

maps := [3]map[string]string{
    make(map[string]string),
    make(map[string]string),
    make(map[string]string),
}

You must call make for each map, otherwise the maps would be uninitialized (nil).

You can also create a slice with 3 (uninitialized) elements with make:

maps := make([]map[string]string, 3)

In this case you'd have to iterate over maps and initialize each element with make.

The simplest solution, in case you're using mgo would be to create a struct for your data:

type Item struct {
    Name string `bson:name`
    Date string `bson:date`
    Qty int `bson:qty`
}

and use it in your array:

var items [3]*Item