I have the following code but it only reads the last part of the JSON value:
public string GetUsersJson(long systemOrgId)
{
var query = #"DECLARE #OrgId bigint = #systemOrgId
SELECT e.OrgId, e.Id, e.FirstName, e.LastName
FROM [Internal].[Employee] e
WHERE OrgId = #OrgId and IsActive=1
FOR JSON PATH, ROOT('Users');";
var json = ExecuteSqlCommandWithJsonResponse(query, systemOrgId);
return json;
}
private string ExecuteSqlCommandWithJsonResponse(string queryString, long systemOrgId)
{
var result = "";
using (SqlConnection connection = new SqlConnection(_systemConnectionString))
{
using (var cmd = connection.CreateCommand())
{
connection.Open();
cmd.CommandText =queryString;
cmd.Parameters.AddWithValue("#systemOrgId", systemOrgId);
using (var reader = cmd.ExecuteReader())
{
while (reader.Read())
{
result = reader.GetString(reader.GetOrdinal("JSON_F52E2B61-18A1-11d1-B105-00805F49916B"));
}
}
}
}
return result;
}
If I use if instead I get the first part.
if (reader.Read())
{
result = reader.GetString(reader.GetOrdinal("JSON_F52E2B61-18A1-11d1-B105-00805F49916B"));
}
According to the SqlDataReader Class documentation a while (reader.Read()) should be used.
https://learn.microsoft.com/en-us/dotnet/api/system.data.sqlclient.sqldatareader?view=dotnet-plat-ext-7.0#examples
Adapting the code to look more like the MS example also gives the same result:
private string ExecuteSqlCommandWithJsonResponse(string queryString, long systemOrgId)
{
var result = "";
using (SqlConnection connection = new SqlConnection(_systemConnectionString))
{
var cmd = connection.CreateCommand();
connection.Open();
cmd.CommandText = queryString;
cmd.Parameters.AddWithValue("#systemOrgId", systemOrgId);
var reader = cmd.ExecuteReader();
while (reader.Read())
{
result = reader.GetString(reader.GetOrdinal("JSON_F52E2B61-18A1-11d1-B105-00805F49916B"));
}
reader.Close();
}
return result;
}
Using a standard concatenate strings with += easily solved it. I hope this can help someone else since this information is missing in the examples I have seen.
https://learn.microsoft.com/en-us/dotnet/csharp/how-to/concatenate-multiple-strings#-and--operators
private string ExecuteSqlCommandWithJsonResponse(string queryString, long systemOrgId)
{
var result = "";
using (SqlConnection connection = new SqlConnection(_systemConnectionString))
{
using (var cmd = connection.CreateCommand())
{
connection.Open();
cmd.CommandText =queryString;
cmd.Parameters.AddWithValue("#systemOrgId", systemOrgId);
using (var reader = cmd.ExecuteReader())
{
while (reader.Read())
{
result += reader.GetString(reader.GetOrdinal("JSON_F52E2B61-18A1-11d1-B105-00805F49916B"));
}
}
}
}
return result;
}
Related
I have a SQL Server 2008 database and I am working on it in the backend. I am working on asp.net/C#
SqlDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
//how do I read strings here????
}
I know that the reader has values. My SQL command is to select just 1 column from a table. The column contains strings ONLY. I want to read the strings (rows) in the reader one by one. How do I do this?
using(SqlDataReader rdr = cmd.ExecuteReader())
{
while (rdr.Read())
{
var myString = rdr.GetString(0); //The 0 stands for "the 0'th column", so the first column of the result.
// Do somthing with this rows string, for example to put them in to a list
listDeclaredElsewhere.Add(myString);
}
}
string col1Value = rdr["ColumnOneName"].ToString();
or
string col1Value = rdr[0].ToString();
These are objects, so you need to either cast them or .ToString().
Put the name of the column begin returned from the database where "ColumnName" is. If it is a string, you can use .ToString(). If it is another type, you need to convert it using System.Convert.
SqlDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
string column = rdr["ColumnName"].ToString();
int columnValue = Convert.ToInt32(rdr["ColumnName"]);
}
while(rdr.Read())
{
string col=rdr["colName"].ToString();
}
it wil work
Thought to share my helper method for those who can use it:
public static class Sql
{
public static T Read<T>(DbDataReader DataReader, string FieldName)
{
int FieldIndex;
try { FieldIndex = DataReader.GetOrdinal(FieldName); }
catch { return default(T); }
if (DataReader.IsDBNull(FieldIndex))
{
return default(T);
}
else
{
object readData = DataReader.GetValue(FieldIndex);
if (readData is T)
{
return (T)readData;
}
else
{
try
{
return (T)Convert.ChangeType(readData, typeof(T));
}
catch (InvalidCastException)
{
return default(T);
}
}
}
}
}
Usage:
cmd.CommandText = #"SELECT DISTINCT [SoftwareCode00], [MachineID]
FROM [CM_S01].[dbo].[INSTALLED_SOFTWARE_DATA]";
using (SqlDataReader data = cmd.ExecuteReader())
{
while (data.Read())
{
usedBy.Add(
Sql.Read<String>(data, "SoftwareCode00"),
Sql.Read<Int32>(data, "MachineID"));
}
}
The helper method casts to any value you like, if it can't cast or the database value is NULL, the result will be null.
For a single result:
if (reader.Read())
{
Response.Write(reader[0].ToString());
Response.Write(reader[1].ToString());
}
For multiple results:
while (reader.Read())
{
Response.Write(reader[0].ToString());
Response.Write(reader[1].ToString());
}
I know this is kind of old but if you are reading the contents of a SqlDataReader into a class, then this will be very handy. the column names of reader and class should be same
public static List<T> Fill<T>(this SqlDataReader reader) where T : new()
{
List<T> res = new List<T>();
while (reader.Read())
{
T t = new T();
for (int inc = 0; inc < reader.FieldCount; inc++)
{
Type type = t.GetType();
string name = reader.GetName(inc);
PropertyInfo prop = type.GetProperty(name);
if (prop != null)
{
if (name == prop.Name)
{
var value = reader.GetValue(inc);
if (value != DBNull.Value)
{
prop.SetValue(t, Convert.ChangeType(value, prop.PropertyType), null);
}
//prop.SetValue(t, value, null);
}
}
}
res.Add(t);
}
reader.Close();
return res;
}
I would argue against using SqlDataReader here; ADO.NET has lots of edge cases and complications, and in my experience most manually written ADO.NET code is broken in at least one way (usually subtle and contextual).
Tools exist to avoid this. For example, in the case here you want to read a column of strings. Dapper makes that completely painless:
var region = ... // some filter
var vals = connection.Query<string>(
"select Name from Table where Region=#region", // query
new { region } // parameters
).AsList();
Dapper here is dealing with all the parameterization, execution, and row processing - and a lot of other grungy details of ADO.NET. The <string> can be replaced with <SomeType> to materialize entire rows into objects.
Actually, I figured it out myself that I could do this:
while (rdr.read())
{
string str = rdr.GetValue().ToString().Trim();
}
In the simplest terms, if your query returns column_name and it holds a string:
while (rdr.Read())
{
string yourString = rdr.getString("column_name")
}
I usually read data by data reader this way. just added a small example.
string connectionString = "Data Source=DESKTOP-2EV7CF4;Initial Catalog=TestDB;User ID=sa;Password=tintin11#";
string queryString = "Select * from EMP";
using (SqlConnection connection = new SqlConnection(connectionString))
using (SqlCommand command = new SqlCommand(queryString, connection))
{
connection.Open();
using (SqlDataReader reader = command.ExecuteReader())
{
if (reader.HasRows)
{
while (reader.Read())
{
Console.WriteLine(String.Format("{0}, {1}", reader[0], reader[1]));
}
}
reader.Close();
}
}
You have to read database columnhere. You could have a look on following code snippet
string connectionString = ConfigurationManager.ConnectionStrings["NameOfYourSqlConnectionString"].ConnectionString;
using (var _connection = new SqlConnection(connectionString))
{
_connection.Open();
using (SqlCommand command = new SqlCommand("SELECT SomeColumnName FROM TableName", _connection))
{
SqlDataReader sqlDataReader = command.ExecuteReader();
if (sqlDataReader.HasRows)
{
while (sqlDataReader.Read())
{
string YourFirstDataBaseTableColumn = sqlDataReader["SomeColumn"].ToString(); // Remember Type Casting is required here it has to be according to database column data type
string YourSecondDataBaseTableColumn = sqlDataReader["SomeColumn"].ToString();
string YourThridDataBaseTableColumn = sqlDataReader["SomeColumn"].ToString();
}
}
sqlDataReader.Close();
}
_connection.Close();
I have a helper function like:
public static string GetString(object o)
{
if (o == DBNull.Value)
return "";
return o.ToString();
}
then I use it to extract the string:
tbUserName.Text = GetString(reader["UserName"]);
I am trying to get int value from the database but It is throwing an error
Unable to cast object of type 'System.Byte' to type 'System.Int32'.
In the database, Active field is tinyint.
Also, how to return both values from this method.
private string CheckData(string firstValue, string SecondValue, int Active)
{
string Data = "";
StringBuilder sb = new StringBuilder();
string query = #"select M.ident Mi, mmp.active Active
from Iden.Iden M
inner join PtM.MPt MMP on MMP.mPat = M.id
where M.ident = 'firstValue'
and Mi.ident = 'SecondValue'";
sb.Append(query);
sb.Replace("firstValue", firstValue);
sb.Replace("SecondValue", SecondValue);
SqlConnection connection = new SqlConnection(connString);
SqlCommand cmd = new SqlCommand(sb.ToString());
cmd.CommandTimeout = 0;
cmd.CommandType = CommandType.Text;
cmd.Connection = connection;
try
{
connection.Open();
SqlDataReader reader = cmd.ExecuteReader();
if (reader.HasRows)
{
while (reader.Read())
{
Data = reader.GetString(reader.GetOrdinal("Mi"));
Active = reader.GetInt32(reader.GetOrdinal("Active"));
}
}
}
catch (Exception ex)
{
_log.Error($"Exception:{ex.Message}");
}
finally
{
connection.Close();
connection.Dispose();
}
return Data;
}
Here's a stab at it. I can't debug it (since I don't feel like creating a database).
First I create a type to hold the results. You could just use a Tuple, but this seems clearer:
public class DataActive
{
public string Data { get; set; }
public byte Active { get; set; }
}
I make your function return a collection of these - it's not obvious from your code that there is only one.
You'll also notice that I use SqlParameters to add firstValue and secondValue to your query. Look up SQL Injection (and Little Bobby Tables).
If you are using a recent version of C# (which I don't), there's a new syntax for using that requires less indenting. The using statements stick a call to Dispose in a finally statement at the end of the block. Also note that I'm disposing the SqlCommand and the DataReader
public static IEnumerable<DataActive> CheckData(string firstValue, string secondValue)
{
var results = new List<DataActive>();
const string query = #"select M.ident Mi,mmp.active Active from Iden.Iden M
Inner join PtM.MPt MMP on MMP.mPat =M.id
where M.ident = #firstValue and Mi.ident = #secondValue";
using (var connection = new SqlConnection(connString))
{
using (var cmd = new SqlCommand(query))
{
cmd.CommandTimeout = 0;
cmd.CommandType = CommandType.Text;
cmd.Connection = connection;
cmd.Parameters.Add("#firstValue", SqlDbType.NVarChar, 50).Value = firstValue;
cmd.Parameters.Add("#secondValue", SqlDbType.NVarChar, 50).Value = secondValue;
try
{
connection.Open();
using (var reader = cmd.ExecuteReader())
{
var dataOrdinal = reader.GetOrdinal("Mi");
var activeOrdinal = reader.GetOrdinal("Active");
if (reader.HasRows)
{
while (reader.Read())
{
results.Add(new DataActive
{
Data = reader.GetString(dataOrdinal),
Active = reader.GetByte(activeOrdinal),
});
}
}
}
}
catch (Exception ex)
{
_log.Error($"Exception:{ex.Message}");
}
}
}
return results;
}
If your TINY_INT Active represents a boolean value, figure out what the rule is, and do a conversion after you get the value using reader.GetByte.
One final note, it's often better to log ex.ToString() rather than ex.Message. You get the message and the stack that way.
I am having problem with SQLDataReader when it comes into situation that I have one row of data, and one or tho columns (fields) have null value.
Can anybody help with this? Null values are related to string, float and datetime datatype.
First method is:
public class SpajanjeCollection:ObservableCollection<Spajanje>
{
public static SpajanjeCollection GetAllSpajanjes()
{
SpajanjeCollection spajanjes = new SpajanjeCollection();
Spajanje spajanje = null;
using (SqlConnection conn = new SqlConnection())
{
conn.ConnectionString = ConfigurationManager.ConnectionStrings["ConnString"].ToString();
conn.Open();
SqlCommand command = new SqlCommand("SELECT Ponude.IdPonude, Ponude.SifraProizvoda, Proizvodi.Naziv, Proizvodi.Opis, Proizvodi.PocetnaCijena, Ponude.PocetakAukcije, Users.UserName, Ponude.PonudjenaCijena, Ponude.ZavrsetakAukcije, Ponude.Status FROM Ponude LEFT OUTER JOIN Users ON Ponude.Kupac = Users.UserName INNER JOIN Proizvodi ON Ponude.SifraProizvoda = Proizvodi.Id", conn);
using (SqlDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
spajanje = Spajanje.GetSpajanjeFromResultSet(reader);
spajanjes.Add(spajanje);
}
}
}
return spajanjes;
}
}
Second method for data reading is:
public static Spajanje GetSpajanjeFromResultSet(SqlDataReader reader)
{
Spajanje spajanje = new Spajanje(Convert.ToInt16(reader["IdPonude"]), Convert.ToInt16(reader["SifraProizvoda"]), Convert.ToString(reader["Naziv"]), Convert.ToString(reader["Opis"]), float.Parse(reader["PocetnaCijena"].ToString()), (DateTime?)reader["PocetakAukcije"], Convert.ToString(reader["UserName"]), float.Parse(reader["PonudjenaCijena"].ToString()), (DateTime?)reader["ZavrsetakAukcije"], Convert.ToString(reader["Status"]));
return spajanje;
}
I have a method for getting data out of my SQL Server database. I'm using a reader to get all the data. The problem is that the reader keeps reading and the application doesn't pop up. It is like an infinite loop or something.
public static List<Reservering> GetReserverings()
{
Reservering res = new Reservering();
using (var conn = new SqlConnection(ConnectionString))
{
conn.Open();
const string query = "select b.boekingid, k.naam, bk.incheckdatum, bk.uitcheckdatum, b.hotelid, b.aantal_gasten from boeking b join klant k on k.klantid = b.boekingid join boekingkamer bk on b.boekingid = bk.boekingid where bk.incheckdatum is not null and bk.uitcheckdatum is not null";
SqlCommand selectReserveringen = new SqlCommand(query, conn);
SqlDataReader reader = selectReserveringen.ExecuteReader();
while (reader.Read())
{
res.Id = (int)reader["boekingid"];
res.Naam = (string)reader["naam"];
res.Incheck_datum = (DateTime)reader["incheckdatum"];
res.Uitcheck_datum = (DateTime)reader["uitcheckdatum"];
res.Hotel = (int)reader["hotelid"];
res.Aantal_personen = (int)reader["aantal_gasten"];
}
reader.Close();
}
return GetReserverings();
}
Does anyone know how to fix this problem?
You've got an infinite recursion by calling the method itself at the end:
return GetReserverings();
You could've discovered this by setting a breakpoint in your method and stepping through your code.
You want to return a list of reservations instead:
var result = new List<Reservering>();
// your code...
return result;
And within your while() loop, you'd want to instantiate a new Reservering each iteration, and Add it to the result list.
You should create an instance of Reservering for each record read and store these instances in the List<Reservering>:
public static List<Reservering> GetReserverings() {
List<Reservering> result = new List<Reservering>();
using (var conn = new SqlConnection(ConnectionString)) {
conn.Open();
const string query =
#"select b.boekingid,
k.naam,
bk.incheckdatum,
bk.uitcheckdatum,
b.hotelid,
b.aantal_gasten
from boeking b join
klant k on k.klantid = b.boekingid join
boekingkamer bk on b.boekingid = bk.boekingid
where bk.incheckdatum is not null
and bk.uitcheckdatum is not null";
using (SqlCommand selectReserveringen = new SqlCommand(query, conn)) {
using (SqlDataReader reader = selectReserveringen.ExecuteReader()) {
while (reader.Read()) {
Reservering res = new Reservering();
result.Add(res);
res.Id = Convert.ToInt32(reader["boekingid"]);
res.Naam = Convert.ToString(reader["naam"]);
res.Incheck_datum = Convert.ToDateTime(reader["incheckdatum"]);
res.Uitcheck_datum = Convert.ToDateTime(reader["uitcheckdatum"]);
res.Hotel = Convert.ToInt32(reader["hotelid"]);
res.Aantal_personen = Convert.ToInt32(reader["aantal_gasten"]);
}
}
}
}
return result;
}
Edit: You can try to simplify while loop with a help of object initializing:
...
while (reader.Read()) {
result.Add(new Reservering() {
Id = Convert.ToInt32(reader["boekingid"]),
Naam = Convert.ToString(reader["naam"]),
Incheck_datum = Convert.ToDateTime(reader["incheckdatum"]),
Uitcheck_datum = Convert.ToDateTime(reader["uitcheckdatum"]),
Hotel = Convert.ToInt32(reader["hotelid"]),
Aantal_personen = Convert.ToInt32(reader["aantal_gasten"])
});
}
public static List<Reservering> GetReserverings()
{
List<Reserving> reservings = new List<Reservings>();
using (var conn = new SqlConnection(ConnectionString))
{
conn.Open();
const string query = "select b.boekingid, k.naam, bk.incheckdatum, bk.uitcheckdatum, b.hotelid, b.aantal_gasten from boeking b join klant k on k.klantid = b.boekingid join boekingkamer bk on b.boekingid = bk.boekingid where bk.incheckdatum is not null and bk.uitcheckdatum is not null";
SqlCommand selectReserveringen = new SqlCommand(query, conn);
SqlDataReader reader = selectReserveringen.ExecuteReader();
while (reader.Read())
{
Reservering res = new Reservering();
res.Id = (int)reader["boekingid"];
res.Naam = (string)reader["naam"];
res.Incheck_datum = (DateTime)reader["incheckdatum"];
res.Uitcheck_datum = (DateTime)reader["uitcheckdatum"];
res.Hotel = (int)reader["hotelid"];
res.Aantal_personen = (int)reader["aantal_gasten"];
reservings.add(res);
}
reader.Close();
}
return reservings;
}
This question is continuation of my previous one. Without going into too much details, I'm filling dataset with 2 related 1-to-many tables.
So, my question now is - why this code works good
public DataAgencyR_DataSet SelectOne(int id)
{
DataAgencyR_DataSet result = new DataAgencyR_DataSet();
using (DbCommand command = Connection.CreateCommand())
{
try
{
command.CommandText = SqlStrings.SelectDataAgencyR_SelectOne();
var param = ParametersBuilder.CreateByKey(command, "ID_DeclAgenc", id, "ID_DeclAgenc");
command.Parameters.Add(param);
Connection.Open();
using (DbDataReader reader = command.ExecuteReader())
{
while (reader.Read())
{
System.Diagnostics.Trace.WriteLine(String.Format("{0}-{1}", reader[0], reader[1]));
}
System.Diagnostics.Trace.WriteLine("-------------");
reader.NextResult();
while (reader.Read())
{
System.Diagnostics.Trace.WriteLine(String.Format("{0}-{1}", reader[0], reader[1]));
}
}
}
catch (DbException e)
{
Logger.Error(e.Message, e);
throw new DataAccessException("Error occurs while SelectOne method porcessed", e);
}
finally
{
if (Connection.State != ConnectionState.Closed) Connection.Close();
}
}
return result;
}
public static string SelectDataAgencyR_SelectOne()
{
return "SELECT a.* FROM t0_DataAgency_R a WHERE a.SetToPartners = 1 AND a.ID_DeclAgenc = #ID_DeclAgenc;" +
"SELECT c.* FROM t01_ChoiceParam_R c JOIN t0_DataAgency_R a on a.ID_DeclAgenc = c.ID_DeclAgenc WHERE SetToPartners = 1 AND a.ID_DeclAgenc = #ID_DeclAgenc";
}
and this is not
public DataAgencyR_DataSet SelectOne(int id)
{
DataAgencyR_DataSet result = new DataAgencyR_DataSet();
using (DbCommand command = Connection.CreateCommand())
{
try
{
command.CommandText = SqlStrings.SelectDataAgencyR_SelectOne();
var param = ParametersBuilder.CreateByKey(command, "ID_DeclAgenc", id, "ID_DeclAgenc");
command.Parameters.Add(param);
Connection.Open();
using (DbDataReader reader = command.ExecuteReader())
{
result.t0_DataAgency_R.Load(reader);
reader.NextResult();
result.t01_ChoiceParam_R.Load(reader);
}
}
catch (DbException e)
{
Logger.Error(e.Message, e);
throw new DataAccessException("Error occurs while SelectOne method porcessed", e);
}
finally
{
if (Connection.State != ConnectionState.Closed) Connection.Close();
}
}
return result;
}
public static string SelectDataAgencyR_SelectOne()
{
return "SELECT a.* FROM t0_DataAgency_R a WHERE a.SetToPartners = 1 AND a.ID_DeclAgenc = #ID_DeclAgenc;" +
"SELECT c.* FROM t01_ChoiceParam_R c JOIN t0_DataAgency_R a on a.ID_DeclAgenc = c.ID_DeclAgenc WHERE SetToPartners = 1 AND a.ID_DeclAgenc = #ID_DeclAgenc";
}
After second example, I have filled only result.t0_DataAgency_R table - but not result.t01_ChoiceParam_R. Why can it be so?
Thanks in advance
DataTable.Load automatically advances the reader to the next result. So you should remove your explicit call to NextResult.
Meaning:
using (DbDataReader reader = command.ExecuteReader())
{
result.t0_DataAgency_R.Load(reader);
result.t01_ChoiceParam_R.Load(reader);
}
Adding a DataSet to the mix... we used to use SqlDataAdapter and returned a DataSet but didn't take advantage of any of the offline features, etc., so a SqlDataReader is a better fit. Here's code to fill a DataSet. Found this was about 10% faster overall.
Dim s As DataSet = New DataSet()
Using reader As SqlDataReader = command.ExecuteReader()
Dim tables As New List(Of DataTable)
Do
Dim table As New DataTable()
table.Load(reader)
tables.Add(table)
s.Tables.Add(table)
Loop While Not reader.IsClosed
s.Load(reader, LoadOption.OverwriteChanges, tables.ToArray())
End Using