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migrating an access multi valued field column to c#

I am attempting to use the Microsoft.ACE.OLEDB.12.0 driver to read data from an access database. came upon an odd situation. one of the columns in the access database shows as a comma delimited list of ids.
Wells
________
345,456,7
6,387
when I looked at the column definition in access I thought it would say string but it does not, it says number. so I guess it is storing an array of integers in a single column?
I'm having a tough time getting a data reader to pick this up.
using
var w = DB_Reader.GetValue(DB_Reader.GetOrdinal("Wells"));
results in the error
The provider could not determine the Object value. For example, the
row was just created, the default for the Object column was not
available, and the consumer had not yet set a new Object value.

Well, at the end of the day, you can think of the mutli-value column as in fact a child table.
So, if you looking to migrate a master and child table, then in YOUR database, you need a relational set of tables to re-create what Access is doing behind the scene.
So, lets take a multi-value example and query.
Say we have this sql query in Access:
SELECT ID, Person_Name, FavorateColors FROM tPerson;
But, "favorite colors" is one of those MV columns. (and I should point out with the HUGE movement towards no-sql databases - they also often work this way also - same for XML or JSON data for that matter. However, be it some XML, JSON or Access mutli-value features? Well, you need that child table if you going to adopt a relational data model to represent this data.
Ok, so we run the above query, and you get this output:
In fact, when I used the lookup wizard - I picked a child table called tblColors.
but, how can we explode the above query to dig out the data?
Change the above query to this:
SELECT ID, Person_Name, FavorateColors.Value FROM tPerson
Note how we added ".value" after the MV column name. Now, when you run the query, you get the SAME result as if you had two tables, and did a left join. The parent table rows will like any relational database simple repeat for each child table value, and you get this:
Note how now the PK value and the row is repeating for each child mv value.
So, you are quite much free to query as per above - you get what amounts to a left joined table, and of course the parent record repeats.
So, just like XML, JSON, or in fact a query or a table of data with repeating parent row, and child rows? Well, you quite much forced to write code to split out this data, or re-normalize the data. This of course is far more common when receiving say JSON/XML data, or in fact often say data from a Excel sheet.
So, you have to process out the child record data, and create a relation for that data.
And thus now our question becomes how can we import JSON/XML/Excel data that really should have used two relational database tables.
So, assuming we want to process this data? You process it the same as for any data you have that should have been two related tables in the first place.
it really depends if this is a one time import, or you have to do this all the time?
If it was a one time deal, then I would use Access, and use a make table query based on the above query. You would in fact have to pluck up the PK ID from the child table. In above there is a child table called colors - we just missing that "junction" table in between that Access automatic created. The hidden tables are not exposed, and thus I would simply use a make table query in access, and then add a FK column that is the PK value from the tblColors.

Conflicts between databases

I have an automation project that I use for several similar sites.
The databases of the sites are also similar beside the USERS table.
In one database the table USERS has the column Fname, in the other one this column is not present. In the other database I have a column named RegesrationDate and in others this column is not present. etc. etc.
When I am running a query I get the error
specified cast is not valid.
because I can't cast the return value (which has more columns then I am holding in my dbml file).
There is a way in my project to make a generic dbml object that I will run:
SELECT * FROM USERS
and to get a normal object. Do you have other ideas how to make my project work?

first approach:
My suggestion is to remove all unique fields and get the generic table at first.
After that, use db.ExecuteQuery for the unique fields every special db.
second:
It's not generic db, therefore use two (or more) user table on your dbml file.
userDb1 table, userDb2 table....
in c# do:
if(dbname == 1){
var a =db.userdb1.select()....
}

Retrieving scalar data using .xsd dataset object?

Can someone suggest the best way to retrieve a scalar value when the site uses .xsd files for the data sets? I have such site where before I commit to a insert task I need to verify duplicates.
Back in the day one would just instantiate a new connection and command object and run the query through BLL/DAL - easy job. With this prepackaged xsd file that the Studio creates for you I have no idea how to do it.
Thanks,
Risho

First, i would recommend to add an unique index in your database to ensure that it's impossible to create duplicates.
To answer your question: you can add queries to the automatically created TableAdapters:
How to: Create TableAdapter queries
From MSDN
TableAdapter with multiple queries
Unlike standard data adapters, TableAdapters can contain multiple
queries to fill their associated data tables. You can define as many
queries for a TableAdapter as your application requires, as long as
each query returns data that conforms to the same schema as its
associated data table. This enables loading of data that satisfies
differing criteria. For example, if your application contains a table
of customers, you can create a query that fills the table with every
customer whose name begins with a certain letter, and another query
that fills the table with all customers located in the same state. To
fill a Customers table with customers in a given state you can create
a FillByState query that takes a parameter for the state value: SELECT
* FROM Customers WHERE State = #State. You execute the query by calling the FillByState method and passing in the parameter value like
this: CustomerTableAdapter.FillByState("WA").
In addition to queries that return data of the same schema as the
TableAdapter's data table, you can add queries that return scalar
*(single) values.* For example, creating a query that returns a count of
customers (SELECT Count(*) From Customers) is valid for a
CustomersTableAdapter even though the data returned does not conform
to the table's schema.

Reading custom data from SQL tables

We have an application that allows the user to add custom columns to our tables (maybe not the best idea, but that's how it is).
We are now (re)designing our dataaccess layer (we didn't really have one before) and now we're going to use parameterized queries in our datamappers when querying the SQL-database (earlier we concatenated the SQL-strings and escaped all input).
Now we're trying to determine the best way of handling the custom columns in order to both query, create and update these records. The custom attributes are going to be stored in a Dictionary on our "business objects" so I was thinking about doing it like this:
Querying data
Use SELECT * to get all columns and populate our properties and store the rest (custom data) in a dictionary on the business object.
Create/Update
Iterate all columns in the table (something like: SELECT COLUMN_NAME FROM information_schema.columns WHERE TABLE_NAME = 'TableName'
Generate a SQL-string (with parameterized variablenames) by checking which columns exists in both the dictionary and the table and then adding the values from the dictionary as variables to the SQLCommand
Or are there any better approches while still using parameterized queries?

If you are adding ad-hoc columns, ORM gets very tricky. In some ways, dropping back to DataTable/DataAdapter (of which I am not a fan) may be an option. Personally, I would look first at other options for storing the custom data:
an xml column
a set of key/value pairs against each record (in a second table)
some other delimited format in a [n]varchar(max)
Do you really have to add columns?

How to read the result of SELECT * from joined tables with duplicate column names in .NET

I am a PHP/MySQL developer, slowly venturing into the realm of C#/SQL Server and I am having a problem in C# when it comes to reading an SQL Server query that joins two tables.
Given the two tables:
TableA:
int:id
VARCHAR(50):name
int:b_id
TableB:
int:id
VARCHAR(50):name
And given the query
SELECT * FROM TableA,TableB WHERE TableA.b_id = TableB.id;
Now in C# I normally read query data in the following fashion:
SqlDataReader data_reader= sql_command.ExecuteReader();
data_reader["Field"];
Except in this case I need to differentiate from TableA's name column, and TableB's name column.
In PHP I would simply ask for the field "TableA.name" or "TableB.name" accordingly but when I try something like
data_reader["TableB.name"];
in C#, my code errors out.
How can fix this? And how can I read a query on multiple tables in C#?

The result set only sees the returned data/column names, not the underlying table. Change your query to something like
SELECT TableA.Name as Name_TA, TableB.Name as Name_TB from ...
Then you can refer to the fields like this:
data_reader["Name_TA"];

To those posting that it is wrong to use "SELECT *", I strongly disagree with you. There are many real world cases where a SELECT * is necessary. Your absolute statements about its "wrong" use may be leading someone astray from what is a legitimate solution.
The problem here does not lie with the use of SELECT *, but with a constraint in ADO.NET.
As the OP points out, in PHP you can index a data row via the "TABLE.COLUMN" syntax, which is also how raw SQL handles column name conflicts:
SELECT table1.ID, table2.ID FROM table1, table;
Why DataReader is not implemented this way I do not know...
That said, a solution to be used could build your SQL statement dynamically by:
querying the schema of the tables you're selecting from
build your SELECT clause by iterating through the column names in the schema
In this way you could build a query like the following without having to know what columns currently exist in the schema for the tables you're selecting from
SELECT TableA.Name as Name_TA, TableB.Name as Name_TB from ...

You could try reading the values by index (a number) rather than by key.
name = data_reader[4];
You will have to experiment to see how the numbers correspond.

Welcome to the real world. In the real world, we don't use "SELECT *". Specify which columns you want, from which tables, and with which alias, if required.

Although it is better to use a column list to remove duplicate columns, if for any reason you want *****, then just use
rdr.item("duplicate_column_name")
This will return the first column value, since the inner join will have the same values in both identical columns, so this will accomplish the task.

Ideally, you should never have duplicate column names, across a database schema. So if you can rename your schema to not have conflicting names.
That rule is for this very situation. Once you've done your join, it is just a new recordset, and generally the table names do go with it.