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• How to get the default value of a column of MS Access Database using C++?

  - by user198750

  This is the sql script I used to create a table in MS Access Database. CREATE TABLE Contracts ( id int NULL DEFAULT 0, sex varchar(255) DEFAULT 'female' NOT NULL ) Now I want to programmatically get the default value of the field: "sex", I know it's 'female' but I don't know how to get it using C++ ADO interface. Below is a snippet of my code: m_pRecordset->Fields->get_Item(vIntegerType, &pvObject); bstrColName = pvObject->GetName(); dtype = pvObject->GetType(); attr = pvObject->GetAttributes();

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• Changing populated DataTable column data types

  - by TonE

  Hi, I have a System.Data.DataTable which is populated by reading a CSV file which sets the datatype of each column to string. I want to append the contents of the DataTable to an existing database table - currently this is done using SqlBulkCopy with the DataTable as the source. However, the column data types of the DataTable need to be changed to match the schema of the target database table, handling null values. I am not very familiar with ADO.NET so have been search for a clean way of doing this? Thanks.

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• Visual Studio 2010 RC and Entity Framework 4 RC Support in the New Version of ADO.NET Data Providers

  Devart has recently announced the release of dotConnect products for Oracle, MySQL, PostgreSQL, and SQLite - ADO.NET providers that offer Entity Framework support, LINQ to SQL support, and contain an ORM model designer for developing LINQ to SQL and EF models based on different database engines.

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• Visual Studio 2010 RC and Entity Framework 4 RC Support in the New Version of ADO.NET Data Providers

  Devart has recently announced the release of dotConnect products for Oracle, MySQL, PostgreSQL, and SQLite - ADO.NET providers that offer Entity Framework support, LINQ to SQL support, and contain an ORM model designer for developing LINQ to SQL and EF models based on different database engines.

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• DataView.RowFilter Vs DataTable.Select() vs DataTable.Rows.Find()

  - by Aseem Gautam

  Considering the code below: Dataview someView = new DataView(sometable) someView.RowFilter = someFilter; if(someView.count > 0) { …. } Quite a number of articles which say Datatable.Select() is better than using DataViews, but these are prior to VS2008. Solved: The Mystery of DataView's Poor Performance with Large Recordsets Array of DataRecord vs. DataView: A Dramatic Difference in Performance Googling on this topic I found some articles/forum topics which mention Datatable.Select() itself is quite buggy(not sure on this) and underperforms in various scenarios. On this(Best Practices ADO.NET) topic on msdn it is suggested that if there is primary key defined on a datatable the findrows() or find() methods should be used insted of Datatable.Select(). This article here (.NET 1.1) benchmarks all the three approaches plus a couple more. But this is for version 1.1 so not sure if these are valid still now. Accroding to this DataRowCollection.Find() outperforms all approaches and Datatable.Select() outperforms DataView.RowFilter. So I am quite confused on what might be the best approach on finding rows in a datatable. Or there is no single good way to do this, multiple solutions exist depending upon the scenario?

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• How do I properly host a WCF Data Service in IIS? Why am I getting errors?

  - by j0rd4n

  I'm playing around with WCF Data Services (ADO.NET Data Services). I have an entity framework model pointed at the AdventureWorks database. When I debug my svc file from within Visual Studio, it works great. I can say /awservice.svc/Customers and get back the ATOM feed I expect. If I publish the service (hosted in an ASP.NET web application) to IIS7, the same query string returns a 500 fault. The root svc page itself works as expected and successfully returns ATOM. The /Customers path fails. Here is what my grants look like in the svc file: public class AWService : DataService<AWEntities> { public static void InitializeService( DataServiceConfiguration config ) { config.SetEntitySetAccessRule( "*", EntitySetRights.All ); config.SetServiceOperationAccessRule( "*", ServiceOperationRights.All ); config.DataServiceBehavior.MaxProtocolVersion = DataServiceProtocolVersion.V2; } } Update: I enabled verbose errors and get the following in the XML message: <innererror> <message>The underlying provider failed on Open.</message> <type>System.Data.EntityException</type> <stacktrace> at System.Data.EntityClient.EntityConnection.OpenStoreConnectionIf( ... ... <internalexception> <message> Login failed for user 'IIS APPPOOL\DefaultAppPool'. </message> <type>System.Data.SqlClient.SqlException</type> <stacktrace> at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, ...

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• Sharepoint OLE DB - field not updateable

  - by Pandincus

  I need to write a simple C# .NET application to retrieve, update, and insert some data in a Sharepoint list. I am NOT a Sharepoint developer, and I don't have control over our Sharepoint server. I would prefer not to have to develop this in a proper sharepoint development environment simply because I don't want to have to deploy my application on the Sharepoint server -- I'd rather just access data externally. Anyway, I found out that you can access Sharepoint data using OLE DB, and I tried it successfully using some ADO.NET: var db = DatabaseFactory.CreateDatabase(); DataSet ds = new DataSet(); using (var command = db.GetSqlStringCommand("SELECT * FROM List")) { db.LoadDataSet(command, ds, "List"); } The above works. However, when I try to insert: using (var command = db.GetSqlStringCommand("INSERT INTO List ([HeaderName], [Description], [Number]) VALUES ('Blah', 'Blah', 100)")) { db.ExecuteNonQuery(command); } I get this error: Cannot update 'HeaderName'; field not updateable. I did some Googling and apparently you cannot insert data through OLE DB! Does anyone know if there are some possible workarounds? I could try using Sharepoint Web Services, but I tried that initially and was having a heck of a time authenticating. Is that my only option?

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• C# exception when calling stored procedure: ORA-01460 - unimplemented or unreasonable conversion req

  - by Taylor L

  I'm trying to call a stored procedure using ADO .NET and I'm getting the following error: ORA-01460 - unimplemented or unreasonable conversion requested The stored procedure I'm trying to call has the following parameters: param1 IN VARCHAR2, param2 IN NUMBER, param3 IN VARCHAR2, param4 OUT NUMBER, param5 OUT NUMBER, param6 OUT NUMBER, param7 OUT VARCHAR2 Below is the C# code I'm using to call the stored procedure: OracleCommand command = connection.CreateCommand(); command.CommandType = CommandType.StoredProcedure; command.CommandText = "MY_PROC"; OracleParameter param1 = new OracleParameter() { ParameterName = "param1", Direction = ParameterDirection.Input, Value = p1, OracleDbType = OracleDbType.Varchar2, Size = p1.Length }; OracleParameter param2 = new OracleParameter() { ParameterName = "param2", Direction = ParameterDirection.Input, Value = p2, OracleDbType = OracleDbType.Decimal }; OracleParameter param3 = new OracleParameter() { ParameterName = "param3", Direction = ParameterDirection.Input, Value = p3, OracleDbType = OracleDbType.Varchar2, Size = p3.Length }; OracleParameter param4 = new OracleParameter() { ParameterName = "param4", Direction = ParameterDirection.Output, OracleDbType = OracleDbType.Decimal }; OracleParameter param5 = new OracleParameter() { ParameterName = "param5", Direction = ParameterDirection.Output, OracleDbType = OracleDbType.Decimal}; OracleParameter param6 = new OracleParameter() { ParameterName = "param6", Direction = ParameterDirection.Output, OracleDbType = OracleDbType.Decimal }; OracleParameter param7 = new OracleParameter() { ParameterName = "param7", Direction = ParameterDirection.Output, OracleDbType = OracleDbType.Varchar2, Size = 32767 }; command.Parameters.Add(param1); command.Parameters.Add(param2); command.Parameters.Add(param3); command.Parameters.Add(param4); command.Parameters.Add(param5); command.Parameters.Add(param6); command.Parameters.Add(param7); command.ExecuteNonQuery(); Any ideas what I'm doing wrong?

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• Typecasting EnityObject

  - by AJ

  Hello, I'm new to C# and am stuck on the following. I have a Silverlight web service that uses LINQ to query a ADO.NET entity object. e.g.: [OperationContract] public List<Customer> GetData() { using (TestEntities ctx = new TestEntities()) { var data = from rec in ctx.Customer select rec; return data.ToList(); } } This works fine, but what I want to do is to make this more abstract. The first step would be to return a List<EntityObject> but this gives a compiler error, e.g.: [OperationContract] public List<EntityObject> GetData() { using (TestEntities ctx = new TestEntities()) { var data = from rec in ctx.Customer select rec; return data.ToList(); } } The error is: Error 1 Cannot implicitly convert type 'System.Collections.Generic.List<SilverlightTest.Web.Customer>' to 'System.Collections.Generic.IEnumerable<System.Data.Objects.DataClasses.EntityObject>'. An explicit conversion exists (are you missing a cast?) What am i doing wrong? Thanks, AJ

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• COM: How to handle a specific exception?

  - by Ian Boyd

  i'm talking to a COM object (Microsoft ADO Recordset object). In a certain case the recordset will return a failed (i.e. negative) HRESULT, with the message: Item cannot be found in the collection corresponding to the requested name or ordinal i know what this error message means, know why it happened, and i how to fix it. But i know these things because i read the message, which fortunately was in a language i understand. Now i would like to handle this exception specially. The COM object threw an HRESULT of 0x800A0CC1 In an ideal world Microsoft would have documented what errors can be returned when i try to access: records.Fields.Items( index ) with an invalid index. But they do not; they most they say is that an error can occur, i.e.: If Item cannot find an object in the collection corresponding to the Index argument, an error occurs. Given that the returned error code is not documented, is it correct to handle a specific return code of `0x800A0CC1' when i'm trying to trap the exception: Item cannot be found in the collection corresponding to the requested name or ordinal ? Since Microsoft didn't document the error code, they technically change it in the future.

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• Oracle Data Provider and casting

  - by mrjoltcola

  I use Oracle's specific data provider, not the Microsoft provider that is being discontinued. The thing I've found about ODP.NET is how picky it is with data types. Where JDBC and other ADO providers just convert and make things work, ODP.NET will throw an invalid cast exception unless you get it exactly right. Consider this code: String strSQL = "SELECT DOCUMENT_SEQ.NEXTVAL FROM DUAL"; OracleCommand cmd = new OracleCommand(strSQL, conn); reader = cmd.ExecuteReader(); if (reader != null && reader.Read()) { Int64 id = reader.GetInt64(0); return id; } Due to ODP.NET's pickiness on conversion, this doesn't work. My usual options are: 1) Retrieve into a Decimal and return it with a cast to an Int64 (I don't like this because Decimal is just overkill, and at least once I remember reading it was deprecated...) Decimal id = reader.GetDecimal(0); return (Int64)id; 2) Or cast in the SQL statement to make sure it fits into Int64, like NUMBER(18) String strSQL = "SELECT CAST(DOCUMENT_SEQ.NEXTVAL AS NUMBER(18)) FROM DUAL"; I do (2), because I feel its just not clean pulling a number into a .NET Decimal when my domain types are Int32 or Int64. Other providers I've used are nice (smart) enough to do the conversion on the fly. Any suggestions from the ODP.NET gurus?

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• How update DB table with DataSet

  - by Paul

  I am begginer with ADO.NET , I try update table with DataSet. O client side I have dataset with one table. I send this dataset on service side (it is ASP.NET Web Service). On Service side I try update table in database, but it dont 't work. public bool Update(DataSet ds) { SqlConnection conn = null; SqlDataAdapter da = null; SqlCommand cmd = null; try { string sql = "UPDATE * FROM Tab1"; string connStr = WebConfigurationManager.ConnectionStrings["Employees"].ConnectionString; conn = new SqlConnection(connStr); conn.Open(); cmd=new SqlCommand(sql,conn); da = new SqlDataAdapter(sql, conn); da.UpdateCommand = cmd; da.Update(ds.Tables[0]); return true; } catch (Exception ex) { throw ex; } finally { if (conn != null) conn.Close(); if (da != null) da.Dispose(); } } Where can be problem?

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• Sharepoint OLE DB - cannot insert records? "Field not updateable" error

  - by Pandincus

  I need to write a simple C# .NET application to retrieve, update, and insert some data in a Sharepoint list. I am NOT a Sharepoint developer, and I don't have control over our Sharepoint server. I would prefer not to have to develop this in a proper sharepoint development environment simply because I don't want to have to deploy my application on the Sharepoint server -- I'd rather just access data externally. Anyway, I found out that you can access Sharepoint data using OLE DB, and I tried it successfully using some ADO.NET: var db = DatabaseFactory.CreateDatabase(); DataSet ds = new DataSet(); using (var command = db.GetSqlStringCommand("SELECT * FROM List")) { db.LoadDataSet(command, ds, "List"); } The above works. However, when I try to insert: using (var command = db.GetSqlStringCommand("INSERT INTO List ([HeaderName], [Description], [Number]) VALUES ('Blah', 'Blah', 100)")) { db.ExecuteNonQuery(command); } I get this error: Cannot update 'HeaderName'; field not updateable. I did some Googling and apparently you cannot insert data through OLE DB! Does anyone know if there are some possible workarounds? I could try using Sharepoint Web Services, but I tried that initially and was having a heck of a time authenticating. Is that my only option?

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• How to estimate size of data to transfer when using DbCommand.ExecuteXXX?

  - by Yadyn

  I want to show the user detailed progress information when performing potentially lengthy database operations. Specifically, when inserting/updating data that may be on the order of hundreds of KB or MB. Currently, I'm using in-memory DataTables and DataRows which are then synced with the database via TableAdapter.Update calls. This works fine and dandy, but the single call leaves little opportunity to glean any kind of progress info to show to the user. I have no idea how much data is passing through the network to the remote DB or its progress. Basically, all I know is when Update returns and it is assumed complete (barring any errors or exceptions). But this means all I can show is 0% and then a pause and then 100%. I can count the number of rows, even going so far to cound how many are actually Modified or Added, and I could even maybe calculate per DataRow its estimated size based on the datatype of each column, using sizeof for value types like int and checking length for things like strings or byte arrays. With that, I could probably determine, before updating, an estimated total transfer size, but I'm still stuck without any progress info once Update is called on the TableAdapter. Am I stuck just using an indeterminate progress bar or mouse waiting cursor? Would I need to radically change our data access layer to be able to hook into this kind of information? Even if I can't get it down to the precise KB transferred (like a web browser file download progress bar), could I at least know when each DataRow/DataTable finishes or something? How do you best show this kind of progress info using ADO.NET?

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• Generic list typecasting problem

  - by AJ

  Hello, I'm new to C# and am stuck on the following. I have a Silverlight web service that uses LINQ to query a ADO.NET entity object. e.g.: [OperationContract] public List<Customer> GetData() { using (TestEntities ctx = new TestEntities()) { var data = from rec in ctx.Customer select rec; return data.ToList(); } } This works fine, but what I want to do is to make this more abstract. The first step would be to return a List<EntityObject> but this gives a compiler error, e.g.: [OperationContract] public List<EntityObject> GetData() { using (TestEntities ctx = new TestEntities()) { var data = from rec in ctx.Customer select rec; return data.ToList(); } } The error is: Error 1 Cannot implicitly convert type 'System.Collections.Generic.List<SilverlightTest.Web.Customer>' to 'System.Collections.Generic.IEnumerable<System.Data.Objects.DataClasses.EntityObject>'. An explicit conversion exists (are you missing a cast?) What am i doing wrong? Thanks, AJ

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• Is this OleDbDataAdapter bug

  - by ????

  It doesn't look to me OleDbDataAdapter should throw an exception on trying to fill DataSet for a db table column of type decimal(28,3). The message is "The numerical value is too large to fit into a 96 bit decimal". Could you just check this, I have no significant experience with ADO.NET and OLE DB components? The VB.NET code we have in the application is this: Dim dbDataSet As New DataSet Dim dbDataAdapter As OleDbDataAdapter Dim dbCommand As OleDbCommand Dim conn As OleDbConnection Dim connectionString As String 'parts where connectionString is set conn = New OleDbConnection(connectionString) 'part where sqlQuery is set but it ends up being "SELECT Price As 'Price' From PricebookView" - Price is of type decimal(28,3) dbCommand = New OleDbCommand(sqlQuery, conn) dbCommand.CommandTimeout = cmdTimeout dbDataAdapter = New OleDbDataAdapter(dbCommand) dbDataAdapter.Fill(dbDataSet) The last line is where the exception is thrown and the top of the stack trace is: at System.Data.ProviderBase.DbBuffer.ReadNumeric(Int32 offset) at System.Data.OleDb.ColumnBinding.Value_NUMERIC() at System.Data.OleDb.ColumnBinding.Value() at System.Data.OleDb.OleDbDataReader.GetValues(Object[] values) at System.Data.ProviderBase.DataReaderContainer.CommonLanguageSubsetDataReader.GetValues(Object[] values) at System.Data.ProviderBase.SchemaMapping.LoadDataRow() at System.Data.Common.DataAdapter.FillLoadDataRow(SchemaMapping mapping) at System.Data.Common.DataAdapter.FillFromReader(DataSet dataset, DataTable datatable, String srcTable, DataReaderContainer dataReader, Int32 startRecord, Int32 maxRecords, DataColumn parentChapterColumn, Object parentChapterValue) at System.Data.Common.DataAdapter.Fill(DataSet dataSet, String srcTable, IDataReader dataReader, Int32 startRecord, Int32 maxRecords) at System.Data.Common.DbDataAdapter.FillInternal(DataSet dataset, DataTable[] datatables, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet) ... I am not sure why does it try to set the value to Int32. Thank you for the time !

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• MVC 2 - Name Attributes on HTML Input Field when using Parent/Child Entities

  - by Click Ahead

  Hi All, I'm pretty new to MVC 2 using the Entity Framework. I have two tables Company {ID int identity PK,Name nvarchar} and User {ID int identity PK,UserName nvarchar,CompanyID int FK}. A Foreign Key exists between User and Company. I generated my ADO.NET Entity Data Model, a Controller and a view to insert a record. My HTML form has the fields Company and UserName and the idea is when I click save a Company and User is inserted into the database. Sounds straight forward right! My question is as follows: I created a strongly-typed view derived from my 'User' entity. I'm using the the html helper Html.TextBoxFor(model = model.Organisation.Name) but the html name attribute for this input field is 'Organisation.Name'. My problem with this is that the dot throws up all sorts of issues in JQuery, which sees this as a property. If I want to change the name I read that I can use DataAnnotations but because I used the Entity Designer this involves using Buddy Classes. Seems like a bit of overkill just to change the html name attribute on this input field. Am I approaching this the right way or am I missing something here? Thanks for the help !

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• Problem using SQLDataReader with Sybase ASE

  - by John K.

  We're developing a reporting application that uses asp.net-mvc (.net 4). We connect through DDTEK.Sybase middleware to a Sybase ASE 12.5 database. We're having a problem pulling data into a datareader (from a stored procedure). The stored procedure computes values (approximately 50 columns) by doing sums, counts, and calling other stored procedures. The problem we're experiencing is... certain (maybe 5% of the columns) come back with NULL or 0. If we debug and copy the SQL statement being used for the datareader and run it inside another SQL tool we get all valid values for all columns. conn = new SybaseConnection { ConnectionString = ConfigurationManager.ConnectionStrings[ConnectStringName].ToString() }; conn.Open(); cmd = new SybaseCommand { CommandTimeout = cmdTimeout, Connection = conn, CommandText = mainSql }; reader = cmd.ExecuteReader(); // AT THIS POINT IMMEDIATELY AFTER THE EXECUTEREADER COMMAND // THE READER CONTAINS THE BAD (NULL OR 0) DATA FOR THESE COLUMNS. DataTable schemaTable = reader.GetSchemaTable(); // AT THIS POINT WE CAN VIEW THE DATATABLE FOR THE SCHEMA AND IT APPEARS CORRECT // THE COLUMNS THAT DON'T WORK HAVE SPECIFICATIONS IDENTICAL TO THE COLUMNS THAT DO WORK Has anyone had problems like this using Sybase and ADO? Thanks, John K.

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• Can I dispose a DataTable and still use its data later?

  - by Eduardo León

  Noob ADO.NET question: Can I do the following? Retrieve a DataTable somehow. Dispose it. Still use its data. (But not send it back to the database, or request the database to update it.) I have the following function, which is indirectly called by every WebMethod in a Web Service of mine: public static DataTable GetDataTable(string cmdText, SqlParameter[] parameters) { // Read the connection string from the web.config file. Configuration configuration = WebConfigurationManager.OpenWebConfiguration("/WSProveedores"); ConnectionStringSettings connectionString = configuration.ConnectionStrings.ConnectionStrings["..."]; SqlConnection connection = null; SqlCommand command = null; SqlParameterCollection parameterCollection = null; SqlDataAdapter dataAdapter = null; DataTable dataTable = null; try { // Open a connection to the database. connection = new SqlConnection(connectionString.ConnectionString); connection.Open(); // Specify the stored procedure call and its parameters. command = new SqlCommand(cmdText, connection); command.CommandType = CommandType.StoredProcedure; parameterCollection = command.Parameters; foreach (SqlParameter parameter in parameters) parameterCollection.Add(parameter); // Execute the stored procedure and retrieve the results in a table. dataAdapter = new SqlDataAdapter(command); dataTable = new DataTable(); dataAdapter.Fill(dataTable); } finally { if (connection != null) { if (command != null) { if (dataAdapter != null) { // Here the DataTable gets disposed. if (dataTable != null) dataTable.Dispose(); dataAdapter.Dispose(); } parameterCollection.Clear(); command.Dispose(); } if (connection.State != ConnectionState.Closed) connection.Close(); connection.Dispose(); } } // However, I still return the DataTable // as if nothing had happened. return dataTable; }

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• How Can I Find What's Causing My Transaction to Get Promoted?

  - by Damian Powell

  I have web site which serves web services (a mixture of .asmx and WCF) which is mostly using LINQ to SQL and System.Transactions. Occaisionally we see the transaction get promoted to a distributed transaction which causes problems because our web servers are isolated from our databases in such a way that it is not possible for us to use MSDTC. I have configured tracing for System.Transactions by adding the following to my web.config: <system.diagnostics> <sources> <source name="System.Transactions" switchValue="Information"> <listeners> <add name="tx" type="System.Diagnostics.XmlWriterTraceListener" initializeData="tx.log" /> </listeners> </source> </sources> </system.diagnostics> It's very interesting and shows me when the transaction is promoted, but I find that it doesn't really help be discover why. Is there an equivalent tracing mechanism for ADO.NET that will show me when connections are created, including the variables that affect pooling (user, cnn string, transaction scope)?

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• Sql Server 2005 multiple insert with c#

  - by bottlenecked

  Hello. I have a class named Entry declared like this: class Entry{ string Id {get;set;} string Name {get;set;} } and then a method that will accept multiple such Entry objects for insertion into the database using ADO.NET: static void InsertEntries(IEnumerable<Entry> entries){ //build a SqlCommand object using(SqlCommand cmd = new SqlCommand()){ ... const string refcmdText = "INSERT INTO Entries (id, name) VALUES (@id{0},@name{0});"; int count = 0; string query = string.Empty; //build a large query foreach(var entry in entries){ query += string.Format(refcmdText, count); cmd.Parameters.AddWithValue(string.Format("@id{0}",count), entry.Id); cmd.Parameters.AddWithValue(string.Format("@name{0}",count), entry.Name); count++; } cmd.CommandText=query; //and then execute the command ... } } And my question is this: should I keep using the above way of sending multiple insert statements (build a giant string of insert statements and their parameters and send it over the network), or should I keep an open connection and send a single insert statement for each Entry like this: using(SqlCommand cmd = new SqlCommand(){ using(SqlConnection conn = new SqlConnection(){ //assign connection string and open connection ... cmd.Connection = conn; foreach(var entry in entries){ cmd.CommandText= "INSERT INTO Entries (id, name) VALUES (@id,@name);"; cmd.Parameters.AddWithValue("@id", entry.Id); cmd.Parameters.AddWithValue("@name", entry.Name); cmd.ExecuteNonQuery(); } } } What do you think? Will there be a performance difference in the Sql Server between the two? Are there any other consequences I should be aware of? Thank you for your time!

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• Deserialization of a DataSet... deal with column name changes? how to migrate data from one column to another?

  - by Brian Kennedy

  So, we wanted to slightly generalize a couple columns in our typed dataset... basically dropped a foreign key constraint and then wanted to change a couple column names to better reflect their new state. All that is easy. The problem is that our users may have serialized out the old version of the DataSet as XML. We want to be able to read those old XML files and deserialize them into the revised DataSet. It seems that would be a fairly common desire... but I haven't yet figured out the right thing to search the internet for. One possible solution would seem to be some way to give a DataColumn an alias or alternate name such that when it reads the old column name, it knows that data can be read into the column with the new column name. I can find no support for any such thing. Another approach would seem to be an "after deserialization" method of some sort... so, I would let it read in the old column values into a normal DataColumn with that name, and then in the "after deserialization" method I would just move the data from the obsolete column into the new column, and then delete the old columns. That would seem to generalize to many other situations... and having such events or hooks is pretty common in ADO.NET. But I have looked for such a hook and haven't yet found it. If no "after deserialization" hook, it would seem I ought to be able to override ReadXml or ReadXmlSerializable methods to call the base and then do my "after" stuff to fix up old data into new. But it does not appear that is possible. Soooo, I have to think backward compatibility with old serialized DataSets and simple data migration would be a well-solved problem... so, trying to reinvent that wheel seems silly. But so far, I haven't seemed to find any documentation on doing those things. Suggestions? What is best practice for this?

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• Why could "insert (...) values (...)" not insert a new row?

  - by nang

  Hi, I have a simple SQL insert statement of the form: insert into MyTable (...) values (...) It is used repeatedly to insert rows and usually works as expected. It inserts exactly 1 row to MyTable, which is also the value returned by the Delphi statement AffectedRows:= myInsertADOQuery.ExecSQL. After some time there was a temporary network connectivity problem. As a result, other threads of the same application perceived EOleExceptions (Connection failure, -2147467259 = unspecified error). Later, the network connection was reestablished, these threads reconnected and were fine. The thread responsible for executing the insert statement described above, however, did not perceive the connectivity problems (No exceptions) - probably it was simply not executed while the network was down. But after the network connectivity problems myInsertADOQuery.ExecSQL always returned 0 and no rows were inserted to MyTable anymore. After a restart of the application the insert statement worked again as expected. For SQL Server, is there any defined case where an insert statment like the one above would not insert a row and return 0 as the number of affected rows? Primary key is an autogenerated GUID. There are no unique or check constraints (which should result in an exception anyway rather than not inserting a row). Are there any known ADO bugs (Provider=SQLOLEDB.1)? Any other explanations for this behaviour? Thanks, Nang.

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• How to Determine the Size of MSADO Command Parameters

  - by Adam

  I am new to MS ADO and trying to understand how to set the size on command parameters as created by the command.CreateParameter (Name, Type, Direction, Size, Value) The documentation says the following: Size Optional. A Long value that specifies the maximum length for the parameter value in characters or bytes. ... If you specify a variable-length data type in the Type argument, you must either pass a Size argument or set the Size property of the Parameter object before appending it to the Parameters collection; otherwise, an error occurs. 1.) What should one pass for fixed-size parameters? Is it a "don't care"? I was a bit confused by the example found here, in which they set size to 3 for an adInteger parameter with Value set to a variant of type VT_I2 pPrmByRoyalty->Type = adInteger; pPrmByRoyalty->Size = 3; pPrmByRoyalty->Direction = adParamInput; pPrmByRoyalty->Value = vtroyal; VT_I2 implies two bytes. A tagVARIANT struct is 16 bytes. How did they land on three? I see that the enum value for adInteger happens to be three, but I suspect that is just a coincidence. So it's a bit confusing what to pass for fixed-size parameters. The team I'm working with has always passed sizeof(int) for adInteger, and it seems to work. Is that correct? Now, for "variable-length" parameters: we are instructed by the documentation to pass "the maximum length .. in characters or bytes". 2.) For adVarChar, is it sufficient to pass the max width as defined in the database? 3.) What about the Wide types (e.g. adVarWChar)? Is it characters or bytes? 4.) How about adVariant, which could contain fixed- or variable-length data? 5.) Do arrays ever come into play here? (we don't pass them as parameters, just curious) Any references or personal insights are welcome.

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• Advice on displaying and allowing editing of data using ASP.NET MVC?

  - by Remnant

  I am embarking upon my first ASP.NET MVC project and I would like to get some input on possible ways to display database data and general best practice. In short, the body of my webpage will show data from my database in a table like format, with each table row showing similar data. For example: Name Age Position Date Joined Jon Smith 23 Striker 18th Mar 2005 John Doe 38 Defender 3rd Jan 1988 In terms of functionality, primarily I’d like to give the user the ability to edit the data and, after the edit, commit the edit to the database and refresh the view.The reason I want to refresh the view is because the data is date ordered and I will need to re-sort if the user edits a date field. My main question is what architecture / tools would be best suited to this fulfil my requirements at a high level? From the research I have done so far my initial conclusions were: ADO.NET for data retrieval. This is something I have used before and feel comfortable with. I like the look of LINQ to SQL but don’t want to make the learning curve any steeper for my first outing into MVC land just yet. Partial Views to create a template and then iterate through a datatable that I have pulled back from my database model. jQuery to allow the user to edit data in the table, error check edited data entries etc. Also, my intial view was that caching the data would not be a key requirement here. The only field a user will be able to update is the field and, if they do, I will need to commit that data to the database immediately and then refresh the view (as the data is date sorted). Any thoughts on this? Alternatively, I have seen some jQuery plug-ins that emulate a datagrid and provide associated functionality. My first thoughts are that I do not need all the functionality that comes with these plug-ins (e.g. zebra striping, ability to sort by column using sort glyph in column headers etc .) and I don’t really see any benefit to this over and above the solution I have outlined above. Again, is there reason to reconsider this view? Finally, when a user edits a date , I will need to refresh the view. In order to do this I had been reading about Html.RenderAction and this seemed like it may be a better option than using Partial Views as I can incorporate application logic into the action method. Am I right to consider Html.RenderAction or have I misunderstood its usage? Hope this post is clear and not too long. I did consider separate posts for each topic (e.g. Partial View vs. Html.RenderAction, when to use jQury datagrid plug-in) but it feels like these issues are so intertwined that they need to be dealt with in contect of each other. Thanks

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