通过单个查询从相关数据库表中回显嵌套的JSON数组？

Question

我有两个数据库表，其中包含有关土地合同的信息。 它们与land_contract_annual_price.land_contract_id > land_contract.land_contract_id 。

表'land_contract'

表“ land_contract_annual_price”

如果土地合同在land_contract_price_type字段中的值为“Rörligtpris”，则表land_contract_annual_price有相关的值。 目前，我正在执行两个查询，每个表一个。 然后，我合并结果并将土地合同显示为嵌套的JSON数组，如下所示：

版本1

[  
 {  
  "land_contract_id":118,
  "land_contract_name":"Avtalsnamn",
  "location_id":71,
  "land_contract_link":"",
  "land_contract_notes":"",
  "land_owner_id":2,
  "land_contract_start_date":"2019-07-25",
  "land_contract_end_date":"2023-07-25",
  "land_contract_terminated":"false",
  "land_contract_payment_interval":"Halv\u00e5rsvis",
  "land_contract_price_type":"R\u00f6rligt \u00e5rspris",
  "land_contract_fixed_annual_price":null,
  "land_contract_annual_prices":[  
    {"year":1, "price":873.00},
    {"year":2, "price":77289.00},
    {"year":3, "price":8.00},
    {"year":4, "price":0.00},
    {"year":5, "price":8729.00}
  ]
 }
]

如果土地合同在land_contract_price_type字段中的值为“ Fast pris”，则表land_contract_annual_price中没有相关的值。 在那种情况下，我会像这样提交土地合同（末尾没有额外的数组）：

版本2

[
 {
  "land_contract_id":13,
  "land_contract_name":null,
  "location_id":null,
  "land_contract_link":"https:\/\/www.something.com\/preview\/Sl%C3%A4pvdam%20Edda\/Kddal\/Bddkta\/Besika%20Markavtal%20%20Halmstad%202016-03-08.pdf?role=personal",
  "land_contract_notes":"",
  "land_owner_id":null,
  "land_contract_start_date":"2016-03-08",
  "land_contract_end_date":"2026-03-08",
  "land_contract_terminated":"true",
  "land_contract_payment_interval":"\u00c5rsvis",
  "land_contract_price_type":"Fast \u00e5rspris",
  "land_contract_fixed_annual_price":"6000.00"
 }
]

我没有想到的是，当我获取所有土地合同时，这种解决方案是不好的。 如果每当一份土地合同在land_contract_price_type字段中的值为“Rörligtpris”，我都会对另一个表进行第二次查询，那么我将进行数百个额外的查询。

当土地合同在land_contract_price_type字段中具有值“Rörligtpris”时，是否有一种方法可以使用一（1）个查询来创建嵌套的JSON数组？

谢谢！

下面是我当前的代码。

function read($pdo, $Id = null, $ResponseMessage = null) {

    $params = [];
    $array = [];

    $sql = "SELECT  lc.Id, lc.Name, lc.LocationId, l.Name AS LocationName, lc.Notes, lc.LandOwnerId, lo.Name AS LandOwnerName, lc.StartDate, lc.EndDate, lc.IsTerminated, lc.PaymentInterval, lc.PriceType, lc.FixedAnnualPrice, lc.Link, lc.Created, lc.Updated, lcap.AnnualPriceYear AS Year, lcap.AnnualPriceAmount AS Amount
            FROM LandContract lc
            LEFT JOIN Location l ON l.Id = lc.LocationId
            LEFT JOIN LandOwner lo ON lo.Id = lc.LandOwnerId
            LEFT JOIN LandContractAnnualPrice lcap ON lcap.LandContractId = lc.Id  
            ORDER BY lc.Id  DESC, lcap.AnnualPriceYear DESC
            ";
    if ($Id) {
        $sql .= 'WHERE lc.Id = ?';
        $params[] = $Id;
    }

    echo $sql;

    $stmt = $pdo->prepare($sql);
    $stmt->execute($params);
    while ($row = $stmt->fetch()) {
        // Fields we want to extract from the select statement into the array 
        $select_fields = ['Id', 'Name', 'LocationId', 'LocationName', 'Link', 'Notes', 'LandOwnerId', 'LandOwnerName',
                            'StartDate', 'EndDate', 'IsTerminated', 'PaymentInterval', 
                            'PriceType', 'FixedAnnualPrice ', 'Created', 'Updated'];

        if (!isset($array[$row['Id']])) {
            // initialize the subarray if it has not been set already 
            $array[$row['Id']] = array_intersect_key($row, array_flip($select_fields));

            if ($row['Year'] != null) {
                $array[$row['Id']]['AnnualPrices'] = [];
            } else {
                $array[$row['Id']]['AnnualPrice'] = $row['FixedAnnualPrice'];
            }
        }

        if ($row['Year'] != null) {
            $array[$row['Id']]['AnnualPrices'][] = ['Year' => $row['Year'], 'Amount' => $row['Amount']];
        }

    }

    if (empty($array)) {
        $ResponseMessage = new ResponseMessage();
        $ResponseMessage->Status = 'Error';
        $ResponseMessage->Message = 'No results';
        echo json_encode($ResponseMessage, JSON_UNESCAPED_UNICODE);
        exit;
    }

    $Response = array();

    if ($ResponseMessage) {
        $Response['Status'] = $ResponseMessage->Status;
        $Response['Message'] = $ResponseMessage->Message;
    }

    $Response['LandContracts'] = array_values($array);

    echo json_encode($Response, JSON_UNESCAPED_UNICODE);

    $stmt = null;
}

Answer 1

最好使用JOIN查询，然后根据结果构造数组-在循环中进行查询通常是一个非常糟糕的主意，并且可以使用JOIN指示符。

您想使用LEFT JOIN ，将它们加入两个表的land_contract_id中。

然后循环您的结果，并构造您的数组，完成后就可以将其编码为JSON字符串。

$params = [];
$array = [];

$sql = "SELECT lc.*, 
               py.land_contract_annual_price_year AS `year`,  
               py.land_contract_annual_price_amount AS `amount`
        FROM land_contract AS lc
        LEFT JOIN land_contract_annual_price AS py 
            ON py.land_contract_id = lc.land_contract_id
        ";
if (isset($_POST['land_contract_id'])) {
    $sql .= 'WHERE lc.land_contract_id = ?';
    $params[] = $_POST["land_contract_id"];
}

$stmt = $pdo->prepare($sql);
$stmt->execute($params);
while ($row = $stmt->fetch()) {
    // Fields we want to extract from the select statement into the array 
    $select_fields = ['land_contract_id', 'land_contract_name', 'location_id', 'land_contract_link', 'land_contract_notes', 'land_owner_id', 
                        'land_contract_start_date', 'land_contract_end_date', 'land_contract_terminated', 'land_contract_payment_interval', 
                        'land_contract_price_type', 'land_contract_fixed_annual_price '];

    if (!isset($array[$row['land_contract_id']])) {
        // initialize the subarray if it has not been set already 
        $array[$row['land_contract_id']] = array_intersect_key($row, array_flip($select_fields));

        if ($row['year'] != null) {
            $array[$row['land_contract_id']]['land_contract_annual_prices'] = [];
        } else {
            $array[$row['land_contract_id']]['land_contract_annual_price'] = $row['land_contract_fixed_annual_price'];
        }
    }

    if ($row['year'] != null) {
        $array[$row['land_contract_id']]['land_contract_annual_prices'][] = ['year' => $row['year'], 'amount' => $row['amount']];
    }

}

if (empty($array)) {
    echo "No results";
    exit;
}

echo json_encode($array, JSON_UNESCAPED_UNICODE);