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• Maintenance window and recovery for a large database

  - by NYSystemsAnalyst

  One of our teams is developing a database that will be somewhat large (~500GB) and grow from there (I know 500 Gigs may seem small to many of you, but it will be one of the larger databases in our shop). One of the issues they are grappling with is backing up and restoring the database. Basically, the database will have several "data" tables and one table used for storing images / documents. We need to accomplish the following: Be able to quickly backup and restore only the data tables (sans images) to our test server for debugging and testing purposes. In the event of a catastrophic database failure, restore the data tables only to get most of the application up and running ASAP. Then, restore the images table when possible. Backup the database within the allotted nightly time window (a few hours). My questions are: Is it possible to accomplish the first two goals while still having the images stored in the same database? If so, would we use filegroups, filestream, or something else? How do other shops backup their databases in a reasonable time window while maintaining high availability? Do you replicate to a second server and backup from there?

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• Regular Expression for Credit Card Track Data

  - by NYSystemsAnalyst

  Are there any known regular expressions out there to validate credit card track 1 and track 2 data? EDIT: Track 1 and Track 2 are the data tracks that are read from credit cards. See the Financial Cards section at http://en.wikipedia.org/wiki/Magnetic_stripe_card

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• Varchar columns: Nullable or not.

  - by NYSystemsAnalyst

  The database development standards in our organization state the varchar fields should not allow null values. They should have a default value of an empty string (""). I know this makes querying and concatenation easier, but today, one of my coworkers questioned me about why that standard only existed for varchar types an not other datatypes (int, datetime, etc). I would like to know if others consider this to be a valid, defensible standard, or if varchar should be treated the same as fields of other data types? I believe this standard is valid for the following reason: I believe that an empty string and null values, though technically different, are conceptually the same. An empty, zero length string is a string that does not exist. It has no value. However, a numeric value of 0 is not the same as NULL. For example, if a field called OutstandingBalance has a value of 0, it means there are $0.00 remaining. However, if the same field is NULL, that means the value is unknown. On the other hand, a field called CustomerName with a value of "" is basically the same as a value of NULL because both represent the non-existence of the name. I read somewhere that an analogy for an empty string vs. NULL is that of a blank CD vs. no CD. However, I believe this to be a false analogy because a blank CD still phyically exists and still has physical data space that does not have any meaningful data written to it. Basically, I believe a blank CD is the equivalent of a string of blank spaces (" "), not an empty string. Therefore, I believe a string of blank spaces to be an actual value separate from NULL, but an empty string to be the absense of value conceptually equivalent to NULL. Please let me know if my beliefs regarding variable length strings are valid, or please enlighten me if they are not. I have read several blogs / arguments regarding this subject, but still do not see a true conceptual difference between NULLs and empty strings.

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• Entity Framework: Setting EntityReference EntityKey causes exception on save

  - by NYSystemsAnalyst

  I have a table with a ModifiedUserID field that is a foreign key to a User table. In entity framework, I'm loading the first table, but not the users table. I have the user ID of the current user, and would like to set the ModifiedUserID to that value for all entities that have been modified prior to saving. Before calling SaveChanges(), I use the ObjectStateManager to get all modified entities. Since I do not have the user object, but I do have the user ID, I set the EntityReference.EntityKey property as follows: entity.UserReference.EntityKey = New EntityKey("MyContainer.User", "UserID", DatabaseUserID) This works fine, but when I execute SaveChanges(), I receive the following error: A relationship is being added or deleted from an AssociationSet 'FK_Table1_User'. With cardinality constraints, a corresponding 'Table1' must also be added or deleted. Now, I see that setting the EntityReference.EntityKey creates a new AssociationSet entry, but how to I prevent this error?

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• Is there a set based solution for this problem?

  - by NYSystemsAnalyst

  We have a table set up as follows: |ID|EmployeeID|Date |Category |Hours| |1 |1 |1/1/2010 |Vacation Earned|2.0 | |2 |2 |2/12/2010|Vacation Earned|3.0 | |3 |1 |2/4/2010 |Vacation Used |1.0 | |4 |2 |5/18/2010|Vacation Earned|2.0 | |5 |2 |7/23/2010|Vacation Used |4.0 | The business rules are: Vacation balance is calculated by vacation earned minus vacation used. Vacation used is always applied against the oldest vacation earned amount first. We need to return the rows for Vacation Earned that have not been offset by vacation used. If vacation used has only offset part of a vacation earned record, we need to return that record showing the difference. For example, using the above table, the result set would look like: |ID|EmployeeID|Date |Category |Hours| |1 |1 |1/1/2010 |Vacation Earned|1.0 | |4 |2 |5/18/2010|Vacation Earned|1.0 | Note that record 2 was eliminated because it was completely offset by used time, but records 1 and 4 were only partially used, so they were calculated and returned as such. The only way we have thought of to do this is to get all of the vacation earned records in a temporary table. Then, get the total vacation used and loop through the temporary table, deleting the oldest record and subtracting that value from the total vacation used until the total vacation used is zero. We could clean it up for when the remaining vacation used is only part of the oldest vacation earned record. This would leave us with just the outstanding vacation earned records. This works, but it is very inefficient and performs poorly. Also, the performance will just degrade over time as more and more records are added. Are there any suggestions for a better solution, preferable set based? If not, we'll just have to go with this.

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• Entity Framework Security

  - by NYSystemsAnalyst

  In my organization, we are just beginning to use the Entity Framework for some applications. In the past, we have pushed developers to utilize stored procedures for all database access. In addition to helping with SQL injection, we tried to grant logins access to stored procedures only to keep security relatively tight. Although inserting, updating, and deleting are easily done through stored procedures in the EF, it appears to be difficult to use stored procedures to query data with EF. However, using LINQ or Entity SQL and allowing EF to create the queries means giving a user read access to the entire database. How have others handled this dilemma?

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