Is there a built-in command which sets a value of a stored key, only if that value is smaller/bigger then some parameter?
Or my only solution here is to make two calls to the cache - one for checking the value, the other one (possible one) for storing a new value?
Thanks
Related
I have a function in C# where db2.case_bill_totals is called three times with different timestamps as parameter and store their value in variable so can use on next step. Is there any way to call that procedure one time and grab all the required data and then save it in variable as per requirement? I hope my provided screenshot will clear my question. Thanks
First I have tried to change the parameter but its not the solution as for this will also need to change the stored procedure, and this call is used in many other places as well.
I coded program that receives value every 3 seconds but I want to only store it if the value is not same as before. For example, if first value was 10001 and second value is 10002 and so on and change interval for these values are not consistent. So it records 10001 and keep reading values after that but only store the value when reading value becomes 10002.
How do I accomplish this?
From what I understand, you are only saving the value if there is a change. You would also need to store the value if your array (or whatever data source you use) is empty.
It may help if you post some code, and give more insight into how you are storing the value.
I have a field in a sqlite database, we'll call it field1, on which I'm trying to iterate over each record (there's over a thousand records). The field type is string. The value of field1 in the first four rows are as follows:
DEPARTMENT
09:40:24
PARAM
350297
Here is some simple code I use to iterate over each row and display the value:
while (sqlite_datareader.Read())
{
strVal = sqlite_datareader.GetString(0);
Console.WriteLine(strVal);
}
The first 3 values display correctly. However, when it gets to the numerical entry 350297 it errors out with the following exception on the .getString() method
An unhandled exception of type 'System.InvalidCastException' occurred in System.Data.SQLite.dll
I've tried casting to a string, and a bunch of other stuff. But I can't get to the bottom of why this is happening. For now, I'm forced to use getValue, which is of type object, then convert back to a string. But I'd like to figure out why getString() isn't working here.
Any ideas?
EDIT: Here's how I currently deal with the problem:
object objVal; // This is declared before the loop starts...
objVal = sqlite_datareader.IsDBNull(i) ? "" : sqlite_datareader.GetValue(i);
if (objVal != "")
{
strVal = (string)objVal;
}
What the question should have included is
The table schema, preferrably the CREATE TABLE statement used to define the table.
The SQL statement used in opening the sqlite_datareader.
Any time you're dealing with data type issues from a database, it is prudent to include such information. Otherwise there is much unnecessary guessing and floundering (as apparent in the comments), when so very useful, crucial information is explicitly defined in the schema DDL. The underlying query for getting the data is perhaps less critical, but it could very well be part of the issue if there are CAST statements and/or other expressions that might be affecting the returned types. If I were debugging the issue on my own system, these are the first thing I would have checked!
The comments contain good discussion, but a best solution will come with understanding how sqlite handles data types straight from the official docs. The key takeaway is that sqlite defines type affinities on a column and then stores actual values according to a limited set of storage classes. A type affinity is a type to which data will attempt to be converted before storing. But (from the docs) ...
The important idea here is that the type is recommended, not required. Any column can still store any type of data.
But now consider...
A column with TEXT affinity stores all data using storage classes NULL, TEXT or BLOB. If numerical data is inserted into a column with TEXT affinity it is converted into text form before being stored.
So even though values of any storage class can be stored in any column, the default behavior should have been to convert any numeric values, like 350297, as a string before storing the value... if the column was properly declared as a TEXT type.
But if you read carefully enough, you'll eventually come to the following at the end of section 3.1.1. Affinity Name Examples:
And the declared type of "STRING" has an affinity of NUMERIC, not TEXT.
So if the question details are taken literally and field1 was defined like field1 STRING, then technically it has NUMERIC affinity and so a value like 350297 would have been stored as an integer, not a string. And the behavior described in the question is precisely what one would expect when retrieving data into strictly-typed data model like System.Data.SQLite.
It is very easy to cuss at such an unintuitive design decisions and I won't defend the behavior, but
at least the results of "STRING" type are clearly stated so that the column can be redefined to TEXT in order to fix the problem, and
"STRING" is actually not a standard SQL data type. SQL strings are instead defined with TEXT, NTEXT, CHAR, NCHAR, VARCHAR, NVARCHAR, etc.
The solution is either to use code as currently implemented: Get all values as objects and then convert to string values... which should be universally possible with .Net objects since they should all have ToString() method defined.
Or, redefine the column to have TEXT affinity like
CREATE TABLE myTable (
...
field1 TEXT,
...
)
Exactly how to redefine an existing column filled with data is another question altogether. However, at least when doing the conversion from the original to the new column, remember to use a CAST(field1 AS TEXT) to ensure the storage class is changed for the existing data. (I'm not certain whether type affinity is "enforced" when simply copying/inserting data from an existing table into another or if the original storage class is preserved by default. That's why I suggest the cast to force it to a text value.)
I have a drop down list which retrieves values from a session I declare as follows.
var autoData = autoRetriever.GetAutoDataByUserId(user.Id);
Session["AutoData"] = autoData;
I then use autoData to populate my drop down list with a “Name” and a int “Value” as indexed in the database. Name and value are both part of my table in the database.
What I am trying to do now is once a user selects from the drop down I am passing the value (e.g 0,1,2,3,n) the id on the db table to a method. OnSelected changed I want to use this value and retrieve another column “Path” from my session (autoData). Namely the path that is associated with the id. Once I have the correct “Path” associated with this value I can move forward with it.
With my OnSelectedIndexChanged method I then have the following. This string selectedAuto contains my value (0,1,2,3,n)
string selectedAuto = AutoDropDown.SelectedValue;
Does anyone have any advice on how I could move forward with this? If I have not explained enough please let me know and I will delve deeper into it.
As #David mentioned yes correct i am trying to use that value to identify that record. That is the part i am finding tricky. How can i retrieve that "Path" based on the value i select.
When using OracleDataReader (Oracle.DataAccess.Client) in a c# program to read data from a recordset are there any situations where the data type in one of the fields could change from row to row ( except DBNull ).
I am thinking of situations like where the select uses a case statement that can return either a value from a column that is a number(9) or a value from a column that is defined as a number(14).
Are there any other gotcha's that might be relevant when up casting the value returned when using the indexer on the data reader e.g. int cityId = (int)dataReader["CityId"]; (except handling DBNull)
AFAIK, data type doesn't change on a row by row basis.
If the query uses a case statement that returns values from different data-types, the engine is responsible to pick the most appropriate to hold values for all, and it will describe the result-set using that data type, as the standard forces to use one data type per column in any result set.
Anyway, if you can't trust/know the source of the query, surround your cast in a try/catch sentence to get any unexpected result and act accordingly.
Each column in the result set will have the same data type and length/size/precision. JDBC connections
Using JDBC, these can actually be obtained from the result set metadata. Not sure whether there is an equivalent for C#
One oddity is a very special user defined type called SYS.ANYTYPE which is mostly used internally for replication. You can have three rows in a result set with one column. The data type of the column would be SYS.ANYTYPE but internally one could have a date value while another has a number and the last has a character. There are special packages for determining what is hidden inside any ANYTYPE value.