How to create JSON array within a JSON array - mysql

Question

3 tables in MYSQL
table_product - product_id, product_name
table_variane - variant_id, variant_name
table_product_variants - product_id, variant_id, MRP, SellPrice
I want to create JSON data out of those in Perl for all the products, in this format:
[
{
"ProductID": "1",
"ProductName": "Green Detergent Bar",
"Variants": [
{
"VariantID": "1",
"VariantName": "500GM",
"MRP": "20.00",
"SellPrice": "19.50"
},
{
"VariantID": "2",
"VariantName": "1KG",
"MRP": "40.00",
"SellPrice": "38.00"
}
]
},
{
"ProductID": "2",
"ProductName": "ABCD",
"Variants": [
{
"VariantID": "3",
"VariantName": "1KG",
"MRP": "200.00",
"SellPrice": "190.50"
},
{
"VariantID": "2",
"VariantName": "1KG",
"MRP": "40.00",
"SellPrice": "38.00"
}
]
}
]
This is Perl Code
my $sql_query = ""; //need to fill this.
my $statement = $db_handle->prepare ($sql_query) or die "Couldn't prepare query '$sql_query': $DBI::errstr\n";
$statement->execute() or die "SQL Error: $DBI::errstr\n";
my #loop_data = ();
while (my #data = $statement->fetchrow_array())
{
my %data = //need to fill this too.
push(#loop_data, \%data);
}
my $json_text = to_json(\#loop_data);
print $json_text;
Please help in filling SQL query and while loop.
Its just a blueprint. Any modification in code is also fine.

Answer 1

That you need arrays (not hashes) complicates things a bit.
Option 1
Use two queries, one that finds the products, and one that finds the variants of a product.
my $product_sth = $dbh->prepare("
SELECT product_id,
product_name
FROM table_product
");
my $variant_sth = $dbh->prepare("
SELECT tv.variant_id,
tv.variant_name,
tvp.MRP,
tvp.SellPrice
FROM table_product_variants AS tpv
JOIN table_variant AS tv
ON tpv.variant_id = tv.variant_id
WHERE tpv.product_id = ?
");
my #data;
while (my $product_row = $product_sth->fetchrow_hashref()) {
my #variants;
$variant_sth->execute($product_row->{product_id});
while (my $variant_row = $variant_sth->fetchrow_hashref()) {
push #variants, {
VariantID => $variant_row->{variant_id},
VariantName => $variant_row->{variant_name},
MRP => $variant_row->{MRP},
SellPrice => $variant_row->{SellPrice},
};
}
push #data, {
ProductID => $product_row->{product_id},
ProductName => $product_row->{product_name},
Variants => \#variants,
};
}
my $data_json = to_json(\#data);
Option 2
Use an HoA to group the variants of a product when using a single query.
my $sth = $dbh->prepare("
SELECT tp.product_id,
tp.product_name,
tv.variant_id,
tv.variant_name,
tvp.MRP,
tvp.SellPrice
FROM table_product AS tp
JOIN table_product_variants AS tpv
ON tp.product_id = tpv.product_id
JOIN table_variant AS tv
ON tpv.variant_id = tv.variant_id
");
my %data;
while (my $row = $sth->fetchrow_hashref()) {
my $product_id = $row->{product_id};
my $product = $data{$product_id} ||= {
ProductID => $row->{product_id},
ProductName => $row->{product_name},
Variants => [],
};
push #{ $product->{Variants} }, {
VariantID => $row->{variant_id},
VariantName => $row->{variant_name},
MRP => $row->{MRP},
SellPrice => $row->{SellPrice},
};
}
my $data_json = to_json([ values(%data) ]);
Option 3
Use sorting to group the variants of a product when using a single query.
my $sth = $dbh->prepare("
SELECT tp.product_id,
tp.product_name,
tv.variant_id,
tv.variant_name,
tvp.MRP,
tvp.SellPrice
FROM table_product AS tp
JOIN table_product_variants AS tpv
ON tp.product_id = tpv.product_id
JOIN table_variant AS tv
ON tpv.variant_id = tv.variant_id
ORDER BY tp.product_id
");
my $last_product_id = 0;
my #data;
while (my $row = $sth->fetchrow_hashref()) {
my $product_id = $row->{product_id};
if ($product_id != $last_product_id) {
$last_product_id = $product_id;
push #data, {
ProductID => $row->{product_id},
ProductName => $row->{product_name},
Variants => [],
};
}
push #{ $data[-1]{Variants} }, {
VariantID => $row->{variant_id},
VariantName => $row->{variant_name},
MRP => $row->{MRP},
SellPrice => $row->{SellPrice},
};
}
my $data_json = to_json(\#data);
It's a little extra work than option 2, but it has the smallest client-side memory footprint (if you didn't have to keep everything in memory).