c# – Dapper.net“where … in”查询不适用于PostgreSQL

发布时间：2020-12-15 08:28:48 所属栏目：百科来源：网络整理

导读：以下查询始终生成错误“42601：语法错误在或接近”$1“ ”. connection.QueryCarStatsProjection( @"select manufacturer,model,year,AVG(price) as averageprice,AVG(miles) as averagemiles,COUNT(*) as count from products where manufacturer IN @manuf

以下查询始终生成错误“42601：语法错误在或接近”$1“
”.

connection.Query<CarStatsProjection>(
                @"select manufacturer,model,year,AVG(price) as averageprice,AVG(miles) as averagemiles,COUNT(*) as count
                        from products
                        where manufacturer IN @manufacturers 
                            AND model IN @models
                            AND year IN @years
                        group by manufacturer,year",new { manufacturers = new[] { "BMW","AUDI" },models = new[] { "M4","A3" },years = new[] { 2016,2015 } });

我通过在下面创建一个方法并在内部调用它来构建SQL查询来解决这个问题.想知道Dapper是否可以使用对象参数来处理这个问题吗？

public static string ToInSql(this IEnumerable<object> values)
    {
        var flattened = values.Select(x => $"'{x}'");
        var flatString = string.Join(",",flattened);

        return $"({flatString})";
    }

解决方法

PostgreSQL IN运算符不支持数组(或任何其他集合)作为参数,只支持普通列表(使用ToInSql方法生成的列表),对于PostgreSQL,您需要使用ANY运算符,如下所示：

SELECT manufacturer,COUNT(*) as count
FROM products
WHERE manufacturer = ANY(@manufacturers)
AND model = ANY(@models)
AND year = ANY(@years)
GROUP BY manufacturer,year

（编辑：李大同）

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