使用单个查询从相关数据库表中回显嵌套的 JSON 数组？

Question

我有两个包含土地合同信息的数据库表。它们与land_contract_annual_price.land_contract_id -> land_contract.land_contract_id 相关。

表'land_contract'

表格'land_contract_annual_price'

如果土地合同在字段land_contract_price_type 中具有值“Rörligt pris”，则表中存在相关值 land_contract_annual_price。目前我正在做两个查询，每个表一个。然后我合并结果并将土地合同呈现为嵌套的 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}
  ]
 }
]

如果土地合同在字段 land_contract_price_type 中的值为“Fast pris”，则表中没有相关值 land_contract_annual_price。在那种情况下，我会像这样呈现土地合同（最后没有额外的数组）：

第 2 版

[
 {
  "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"
 }
]

我没想到的是，当我获取所有土地合同时，这个解决方案很糟糕。如果每当土地合同在land_contract_price_type 字段中的值为“Rörligt pris”时，我要对另一个表进行第二次查询，我将进行数百次额外查询。

当土地合同在 land_contract_price_type 字段中的值为“Rörligt pris”时，是否有办法通过一 (1) 个查询创建嵌套 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

您最好使用JOIN 查询，然后根据结果构造您的数组 - 在循环中进行查询通常是一个非常糟糕的主意，并且表明您可以使用JOIN 代替。

您想使用LEFT JOIN，将它们连接到两个表中的land_contract_id。

然后循环你的结果，并构造你的数组，一旦完成，你就可以将它编码成一个 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);