Inserting array of custom types into postgres

Question

I'm trying to insert a row with a column that is an array of a custom type (ingredient). My tables are:

CREATE TYPE ingredient AS (
    name text,
    quantity text,
    unit text
);

CREATE TABLE IF NOT EXISTS recipes (
    recipe_id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
    name text,
    ingredients ingredient[],
    // ...
);

Using raw sql, I can insert a row by:

INSERT INTO recipes (name, ingredients) VALUES ('some_name', ARRAY[ROW('aa', 'bb', 'cc'), ROW('xx', 'yy', 'zz')]::ingredient[] );

But I'm struggling to do this in go with the pq lib. I've created a pq.Array interface:

type Ingredient struct {
    Name string
    Quantity string
    Unit string
}

type Ingredients []*Ingredient

func (ings *Ingredients) ConvertValue(v interface{}) (driver.Value, error) {
    return "something", nil
}
func (ings *Ingredients) Value() (driver.Value, error) {
    val := `ARRAY[]`
    for i, ing := range ings {
        if i != 0 {
            val += ","
        }
        val += fmt.Printf(`ROW('%v','%v','%v')`, ing.Name, ing.Quantity, ing.Unit)
    }
    val += `::ingredient[]`
    return val, nil
}


// and then trying to insert via:
stmt := `INSERT INTO recipes (
        name,
        ingredients
    )
    VALUES ($1, $2)
`
_, err := db.Exec(stmt,
    "some_name",
    &Ingredients{
        &Ingredient{"flour", "3", "cups"},
    },
)

But pg keeps throwing the error:

  Error insertingpq: malformed array literal: "ARRAY[ROW('flour','3','cups')]::ingredient[]"

Am I returning an incorrect driver.Value?

Did you try leaving out the conversion from the driver.Value and adding it to the query? e.g. $2::ingredients[]. — mkopriva
– mkopriva, Commented Dec 3, 2017 at 18:58

mkopriva · Accepted Answer · 2017-12-03 20:14:34Z

You can either use this approach outlined here: https://github.com/lib/pq/issues/544

type Ingredient struct {
    Name string
    Quantity string
    Unit string
}

func (i *Ingredient) Value() (driver.Value, error) {
    return fmt.Sprintf("('%s','%s','%s')", i.Name, i.Quantity, i.Unit), nil
}

stmt := `INSERT INTO recipes (name, ingredients) VALUES ($1, $2::ingredient[])`

db.Exec(stmt, "some_name", pq.Array([]*Ingredient{{"flour", "3", "cups"}}))

Or if you have records in the table and you query it, you will probably see the ingredient array in its literal form, which you can than mimic during insert.

func (ings *Ingredients) Value() (driver.Value, error) {
    val := `{`
    for i, ing := range ings {
        if i != 0 {
            val += ","
        }
        val += fmt.Sprintf(`"('%s','%s','%s')"`, ing.Name, ing.Quantity, ing.Unit)
    }
    val += `}`
    return val, nil
}

// e.g. `{"('flour','3','cups')"}`

stmt := `INSERT INTO recipes (name, ingredients) VALUES ($1, $2::ingredient[])`

// ...

Harald Nordgren · Accepted Answer · 2017-12-03 19:21:48Z

0

It seems your database design is very complicated and not taking into account the strengths (and weaknesses) of SQL.

May I suggest you split the ingredients into their own table with a reference to the recipe. Then finding out a full recipe is a JOIN operation.

Creating the DB:

CREATE TABLE ingredients (
    recipe_id uuid,
    name text,
    quantity int,
    unit text
);

CREATE TABLE recipes (
    recipe_id uuid PRIMARY KEY,
    name text
);

Inserting a recipe and querying to read it out:

INSERT INTO recipes VALUES (
  '5d1cb631-37bd-46cc-a278-4c8558ed8964', 'cake1'
);

INSERT INTO ingredients (recipe_id, name, quantity, unit) VALUES
  ('5d1cb631-37bd-46cc-a278-4c8558ed8964', 'flour', 3, 'cups'),
  ('5d1cb631-37bd-46cc-a278-4c8558ed8964', 'water', 1, 'cups')
;

SELECT r.name, i.name, i.quantity, i.unit
FROM ingredients AS i
INNER JOIN recipes AS r
ON r.recipe_id=i.recipe_id;

SQLFiddle link: http://sqlfiddle.com/#!17/262ad/14

edited Dec 3, 2017 at 19:21

answered Dec 3, 2017 at 19:03

Harald Nordgren

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2 Comments

cat-t Over a year ago

I'm considering doing so at this point. Only reason I wasn't before was because I just needed a simple array without the need to access individual items or search by individual items.

Lev Over a year ago

This is unnecessary complex if one wants to store a simple array. JOIN operations are not free comparing to having a column with arrays.

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