日期时间 null 如何在 json .net 5 Z547594DC437B740C7BD34B81E7DC78

Question

In blazor client side + api

Just to be clear: I want it as generic as possible so this one method in controller executes a stored procedure that can query many tables and return different result sets without knowing of type that this will be parsed into later in frontend wasm. So I cannot return List<MYclass> because it will be different every time.

In api controller I have like this to serialize table that have 3 columns

ID,  IDSiec,  data

The data is datetime type, and I serialize this dataTable like this

da.Fill(dt);
connection.Close();

List<Dictionary<string, object>> rows = new List<Dictionary<string, object>>();

foreach (DataRow dr in dt.Rows)
{
    var row = new Dictionary<string, object>();

    foreach (DataColumn col in dt.Columns)
    {
        row.Add(col.ColumnName, dr[col]);
    }

    rows.Add(row);
}

return Ok(rows);

and then in wasm

class MYclass
{
        public int ID { get; set; }
        public int IDSiec { get; set; }
        public DateTime? data { get; set; }
}
.....

await response.Content.ReadFromJsonAsync<List<MYclass>>());

And if in database all records have this data filed then it is ok but if this data is null then in json for this record I get

"Data":{},

and it fails with an error

The JSON value could not be converted to System.Nullable [System.DateTime]. Path: $[0].Data | LineNumber: 0

How should I handle this kind of situation? Force somehow this serializer to send NULL. Object is not nulable so thats why it sends {} instead of null value probably

Sample json out

[{"ID":1141818,"IDSiec":94,"Data":{},...}]

Thanks and regards

Answer 1

foreach (DataColumn col in dt.Columns)
{
    if (dr[col] != null)  // or test against DbNull or something
    {
       row.Add(col.ColumnName, dr[col]);
    }
}

the final answer from the comment below:

 if (dr[col] == DBNull.Value) 
    row.Add(col.ColumnName, null); 
 else 
   row.Add(col.ColumnName, dr[col]); 

I do agree with the safety concerns raised here. But this answer is about how to handle NULL values from a Db API.