ado.net

问题 I'm updating an existing application which uses a factory to build prepared statements, and then execute them later, which works for the rest of the system, but I've been tasked with adding a call to a statement which uses an NText, and I cannot figure out how to properly prepare the statement. I am getting a runtime error of "SqlCommand.Prepare method requires all variable length parameters to have an explicitly set non-zero Size." but I'm not sure what value to use for the Length Obligatory

问题 I have a one-to-many relationship within my class model. Example: A single role can have many permissions attached to it. so have two table one from the role and one for the permissions for each role. Now i have a role class which in turn has a permission list as a member of that class. When i need to do an update, i instantiate a transactionscope object, and do an update for the role. After that is done and with the transactionscope still open, i open another transactionscope for each

问题 Since I have a "DB util" class with a DataSet QueryDB(string spName, DBInputParams inputParams) method which I use for all my calls to the database, I would like to reuse this method in order to support transacted calls. So, at the end I will have a SqlDataAdapter.Fill within a SqlTransaction. Will this be a bad practice? Because rarely I see usage of DataAdapter.Fill within a transaction and more often ExecuteReader(). Is there any catch? Edit1: The thing is that inside my transaction is

问题 Say a DataGridView has its DataSource property set to a DataView instance. DataGridView dgv; DataTable dt; // ... dt gets populated. DataView dv = dt.DefaultView; dgv.DataSource = dv; // ... dt gets modified // The DataGridView needs to update to show these changes visually // What goes here? I know you could set dgv.DataSource to null , then back to dv . But that seems pretty weird. I'm sure there are a couple of other ways, too. But what's the correct, official way to do this? 回答1: The

问题 I have an object like the below but with a huge amount of data, we observed that it takes a long to be inserted into our SQL database as we were using normal foreach , the main idea is to insert each Department and get the generated identity number, then insert the nested employees assigned with that department ID. <Sample> <Departments> <Department> <Name>HR</Name> <Employees> <Employee> <Name>Marco</Name> </Employee> <Employee> <Name>John</Name> </Employee> <Employee> <Name>Sarah</Name> <

问题 I used a dataset to store 15 tables that I need at the time of loading. When i filled all the tables using stored procedure it returns me all the table but name of the table doesn't comes as that of actual table name in a database. It takes all the table with table name as Table1, Table2, Table3... I want them to be with the name as they actually are in table. SELECT PK_GUEST_TYPE, [DESCRIPTION] FROM L_GUEST_TYPE SELECT PK_AGE_GROUP_ID, AGE_GROUP FROM L_AGE_GROUP SELECT PK_COMPANY_ID, COMPANY

问题 I want to be able to enter SQL into a textbox and display the results in a WPF Datagrid. I thought to start with an SqlDataReader , and set the datagrid's ItemsSource to the data reader: using (var cmd = conn.CreateCommand()) { cmd.CommandText = sql.Text; sqlResults.ItemsSource = cmd.ExecuteReader(); } but this fails with the following error: Invalid attempt to call FieldCount when reader is closed , which I understand to mean that by the time WPF gets around to reading the FieldCount

问题 This is my connection to an access database in .NET: OdbcConnection conn = new OdbcConnection("Driver={Microsoft Access Driver (*.mdb)};Dbq=" + path + "\\Access.mdb;Uid=;Pwd=;"); And I got this problem: base {System.Data.Common.DbException} = {"ERROR [IM002] [Microsoft][ODBC Driver Manager] Data source name not found and no default driver specified"} I have tried couple of database connection strings from here: http://www.connectionstrings.com/access but none of them working. Any suggestions

问题 I am having two entities BusinessUser { Id(PK), Name,...} Login { BusinessUserID(PK, FK), Email, Password, etc...} Relationship between BusinessUser and Login is one-to-zero/one . I am having following configurations In BusinessUser EF configuration class this.HasOptional(bu => bu.LoginInfo) .WithOptionalPrincipal(l => l.BusinessUser); In Login EF configuration class this.HasRequired(l => l.BusinessUser) .WithOptional(bu => bu.LoginInfo); I am getting following exception The navigation

问题 I have got this code below: Dim lJobName As String = "" SQLCommand.CommandText = "Select JobName from Jobs where Id = @Id " SQLCommand.Parameters.Add(New SqlParameter("@Id", SqlDbType.Int)) SQLCommand.Parameters(0).Value = var_id lJobName = SQLCommand.ExecuteScalar() Issue how to catch if no records are found? 回答1: I try to avoid comparing a string to Nothing, even though it does work in VB. The Visual Basic .NET runtime evaluates Nothing as an empty string; that is, "". The .NET Framework,