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Golang JSON: Handling Nested Arrays with Unmarshalling
In Go, when working with nested JSON arrays after unmarshalling, it's crucial to understand the error "type interface {} does not support indexing." This error arises when you attempt to access an element within a JSON array stored in an interface{} variable.
To resolve this issue, you'll need to utilize type assertions to convert the interface{} variable to the underlying array type.
Interface{} Representation in JSON Module
The JSON module represents arrays as []interface{} slices and dictionaries as map[string]interface{} maps when decoding into an interface{} variable.
Accessing Nested Elements with Type Assertions
Without error checking, you can navigate the JSON array using type assertions as follows:
<code class="go">objects := result["objects"].([]interface{}) first := objects[0].(map[string]interface{}) fmt.Println(first["ITEM_ID"])</code>
However, it's important to note that these type assertions can panic if the types do not match. To avoid this issue, you can use the two-return form and check for the error:
<code class="go">objects, ok := result["objects"].([]interface{}) if !ok { // Handle error here }</code>
Decoding into a Structure for Improved Access
If the JSON data follows a consistent format, a more efficient solution is to decode it into a structured type. For instance, based on the provided data:
<code class="go">type Result struct { Query string `json:"query"` Count int `json:"count"` Objects []struct { ItemId string `json:"ITEM_ID"` ProdClassId string `json:"PROD_CLASS_ID"` Available int `json:"AVAILABLE"` } `json:"objects"` }</code>
By decoding into this structure, you can directly access the item ID using result.Objects[0].ItemId. This approach eliminates the need for type assertions and provides a type-safe method for accessing nested elements.
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