Error Retrieving Objects Query Identifier Command .execute From Database
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SQL queries¶ When the model query APIs don't go far enough, you can fall back to writing raw SQL. Django gives you two ways of performing raw SQL queries: you can use Manager.raw() to perform raw queries and return model instances, or you can avoid the model layer entirely and execute custom SQL directly. Warning You should be very careful whenever you write raw SQL. Every time you use it, you should properly escape any parameters that the user can control by using params in order to protect against SQL injection attacks. Please read more about SQL https://db.apache.org/derby/docs/10.2/ref/rrefexcept71493.html injection protection. Performing raw queries¶ The raw() manager method can be used to perform raw SQL queries that return model instances: Manager.raw(raw_query, params=None, translations=None)¶ This method takes a raw SQL query, executes it, and returns a django.db.models.query.RawQuerySet instance. This RawQuerySet instance can be iterated over just like a normal QuerySet to provide object instances. This is best illustrated with an example. Suppose you https://docs.djangoproject.com/en/1.10/topics/db/sql/ have the following model: class Person(models.Model): first_name = models.CharField(...) last_name = models.CharField(...) birth_date = models.DateField(...) You could then execute custom SQL like so: >>> for p in Person.objects.raw('SELECT * FROM myapp_person'): ... print(p) John Smith Jane Jones Of course, this example isn't very exciting - it's exactly the same as running Person.objects.all(). However, raw() has a bunch of other options that make it very powerful. Model table names Where did the name of the Person table come from in that example? By default, Django figures out a database table name by joining the model's "app label" - the name you used in manage.py startapp - to the model's class name, with an underscore between them. In the example we've assumed that the Person model lives in an app named myapp, so its table would be myapp_person. For more details check out the documentation for the db_table option, which also lets you manually set the database table name. Warning No checking is done on the SQL statement that is passed in to .raw(). Django expects that the statement will return a set of rows from the database, but does
Oracle Data Provider for .NET Enabling Updates to the Database Inserting, Deleting, and Updating Data Using the Command Object To view, edit, insert or delete data in a database, you must encapsulate a request https://docs.oracle.com/cd/B28359_01/appdev.111/b28844/building_odp.htm in an OracleCommand object specifying a SQL command, stored procedure, or table name. The OracleCommand object creates the request, sends it to the database, and returns the result. To use the command object: Make two copies of Form1.xx, from application HR_Connect_xx in Chapter 3, "Building a Simple .NET Application Using ODP.NET". To make copies, see the instructions in Appendix B, "Copying a Form". Name the copies error retrieving Form2.cs or Form2.vb and Form3.cs or Form3.vb. The first copy is for the first part of the chapter, and the second copy for the second part of the chapter Open Form2.cs or Form2.vb. Note that the actual form in the designer still says Form1, as you renamed code files but not the actual form controls within the project. Create a string that represents the SQL query and add to error retrieving objects the body of the try statement. The new code is in bold typeface. Visual C#: try { conn.Open(); connect.Enabled = false; // SQL Statement string sql = "select department_name from departments" + " where department_id = 10"; } Visual Basic: Try conn.Open() connect.Enabled = False Dim sql As String = "select department_name from departments" & _ "where department_id = 10" Use the new sql variable to create the OracleCommand object, and set the CommandType property to run a text command. Visual C#: try { conn.Open(); connect.Enabled = false; // SQL Statement string sql = "select department_name from departments" + " where department_id = 10"; OracleCommand cmd = new OracleCommand(sql, conn); cmd.CommandType = CommandType.Text; } Visual Basic: Try conn.Open() connect.Enabled = False Dim sql As String = "select department_name from departments" & _ "where department_id = 10" Dim cmd As New OracleCommand(sql, conn) cmd.CommandType = CommandType.Text Save your work. Retrieving Data: a Simple Query This section demonstrates retrieving data from the database. The ExecuteReader() method of an OracleCommand object returns an OracleDataReader object, which can be accessed to display the result on the form. The application uses a ListBox to display the results. To retrieve data: Create an OracleDataReader object, by adding the code ind