Binding validations does not work when request body is Array of objects

Question

Gin's request validation feature is not working when the request body (JSON) represents an array of objects

Ex:

[ 
   { 
      "field1":"aaa",
      "field2":"bbb"
   }
]

code:

type item struct {
    Field1 string `json:"field1" binding:"required"`
    Field2 string `json:"field2" binding:"required"`
}

var items []item

err := c.BindJSON(&items)

To be more clear, the validation logic in gin is expecting the root object to be a struct and hence bails out when an array type gets passed.

what is best way to validate each object in an array passed in the body?

score 1 · Accepted Answer · answered Oct 28 '19 at 14:13

The JSON will be parsed here and then validated here.

The comment on the default ValidateStruct method:

ValidateStruct receives any kind of type, but only performed struct or pointer to struct type.

You can work around this by defining a struct, as it is needed, that holds your data:

type itemHolder struct {
    Items []item
}

Then defining a custom Unmarshaler, like this:

func (i *itemHolder) UnmarshalJSON(b []byte) error {
    return json.Unmarshal(b, &i.Items)
}

Now *itemHolder implements json.Unmarshaler, which means in turn that it will be a struct that is supported by gin.

This code should work now:

var items itemHolder

err := c.BindJSON(&items)
if err != nil {
    // handle...
}

// use items.Items from here on

Please note that your marshal behaviour will change; so you should definitely implement the Marshaler interface if you need to.

Binding validations does not work when request body is Array of objects

1 Answers1