如何将slice元素传递给函数

Question

I'm in the process of cleaning some code up and am trying to pass a slice value which is a struct to a function.

My struct looks like this:

type GetRecipesPaginatedResponse struct {
    Total       int         `json:"total"`
    PerPage     int         `json:"per_page"`
    CurrentPage int         `json:"current_page"`
    LastPage    int         `json:"last_page"`
    NextPageURL string      `json:"next_page_url"`
    PrevPageURL interface{} `json:"prev_page_url"`
    From        int         `json:"from"`
    To          int         `json:"to"`
    Data        []struct {
        ID               int       `json:"id"`
        ParentRecipeID   int       `json:"parent_recipe_id"`
        UserID           int       `json:"user_id"`
        Name             string    `json:"name"`
        Description      string    `json:"description"`
        IsActive         bool      `json:"is_active"`
        IsPublic         bool      `json:"is_public"`
        CreatedAt        time.Time `json:"created_at"`
        UpdatedAt        time.Time `json:"updated_at"`          
        BjcpStyle struct {
            SubCategoryID   string `json:"sub_category_id"`
            CategoryName    string `json:"category_name"`
            SubCategoryName string `json:"sub_category_name"`
        } `json:"bjcp_style"`
        UnitType struct {
            ID   int    `json:"id"`
            Name string `json:"name"`
        } `json:"unit_type"`
    } `json:"data"`
}

In my code, I fetch some JSON data from an API and get a response back that contains about 100 items in the Data slice.

I am then looping over each item in the Data slice and processing them.

As an example, it looks something like this:

for page := 1; page < 3; page++ {
    newRecipes := getFromRecipesEndpoint(page, latestTimeStamp) //this returns an instance of GetRecipesPaginatedResponse

    for _, newRecipe := range newRecipes.Data {

        if rowExists(db, "SELECT id from community_recipes WHERE id=@id", sql.Named("id", newRecipe.ID)) {
            insertIntoRecipes(db, true, newRecipe)
        } else {
            insertIntoRecipes(db, false, newRecipe)
        }
    }
}

So I am trying to pass the instance of a recipe to the insertIntoRecipes function, which looks like this:

func insertIntoRecipes(db *sql.DB, exists bool, newRecipe GetRecipesPaginatedResponse.Data) {
    if exists {
        //update the existing record in the DB
        //perform some other updates with the information
    } else {
        //insert a new record into the DB
        //insert some other information using this information
    }
}

When I run this, I get the error:

GetRecipesPaginatedResponse.Data undefined (type GetRecipesPaginatedResponse has no method Data)

I can tell that the issue is to do with how I am trying to pass the newRecipe to the insertIntoRecipes function, newRecipe GetRecipesPaginatedResponse.Data, however I am not quite sure how to pass it in and declare the right variable type.

To pass an item inside the Data slice to a function, when I am looping over each item of the Data slice, how do I do that?

Answer 1

You cannot reference the anonymous type of the Data field using a field selector. The fix is to declare a named type for the Data field:

type GetRecipesPaginatedResponse struct {
    ...
    Data        []DataItem
    ...
}

type DataItem struct {
    ID               int       `json:"id"`
    ParentRecipeID   int       `json:"parent_recipe_id"`
    UserID           int       `json:"user_id"`
    Name             string    `json:"name"`
    ...
}

Use it like this:

func insertIntoRecipes(db *sql.DB, exists bool, newRecipe DataItem) {
    ...
}

There's probably a better name for DataItem.