我正在使用Dapper从SQL Server读取数据。我有一条返回长Json结果的SQL语句,但问题是该结果被分为3行,每行最多2033个字符,因此Dapper无法解析返回的结果,因为它是无效的Json。
如何防止这种分裂或如何使Dapper应对呢?
这是我的代码:
SqlMapper.ResetTypeHandlers();
SqlMapper.AddTypeHandler(new JsonTypeHandler<List<Product>>());
const string sql = @"SELECT
*,
(SELECT * FROM Balance b
WHERE p.SKU = b.SKU
FOR JSON PATH) AS [Balances]
FROM Product p
WHERE SKU IN @SKUs
FOR JSON PATH";
var connection = new SqlConnection("myconnection");
return connection.QuerySingleAsync<List<Product>>(sql, new{SKUs = new[] {"foo", "bar"}} });
以及TypeHandler的代码:
public class JsonTypeHandler<T> : SqlMapper.TypeHandler<T>
{
public override T Parse(object value)
{
return JsonConvert.DeserializeObject<T>(value.ToString());
}
public override void SetValue(IDbDataParameter parameter, T value)
{
parameter.Value = JsonConvert.SerializeObject(value);
}
}
这是我如何在DataGrip中运行此SQL 编辑: 这是错误消息:
Newtonsoft.Json.JsonSerializationException:反序列化对象时,意外结束。路径'[0] .Balances [4] .WarehouseId',第1行,位置2033。
答案 0 :(得分:0)
我的解决方案是编写另一种扩展方法,该方法包装如下的Query<string>
方法:
public static T QueryJson<T>(this IDbConnection cnn, string sql, object param = null,
IDbTransaction transaction = null, bool buffered = true, int? commandTimeout = null,
CommandType? commandType = null) where T: class
{
var result = cnn.Query<string>(sql, param, transaction, buffered, commandTimeout, commandType).ToList();
if (!result.Any())
return default(T);
// Concats
var sb = new StringBuilder();
foreach (var jsonPart in result)
sb.Append(jsonPart);
var settings = new JsonSerializerSettings
{
// https://github.com/danielwertheim/jsonnet-contractresolvers
// I use this Contract Resolver to set data to private setter properties
ContractResolver = new PrivateSetterContractResolver()
};
// Using Json.Net to de-serialize objects
return JsonConvert.DeserializeObject<T>(sb.ToString(), settings);
}
当查询大数据(1000个对象花费2.7秒而不是1.3秒)时,此解决方案效果很好,并且慢于多重映射方法。