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  • How to choose between UUIDs, autoincrement/sequence keys and sequence tables for database primary keys?

    - by Tim
    I'm looking at the pros and cons of these three primary methods of coming up with primary keys for database rows. So assuming I am using a database that supports more than one of these methods, is there a simple heuristic to determine what the best option would be for me? How do considerations such a distributed/multiple masters, performance requirements, ORM use, security and testing have on the choice? Any unexpected drawbacks that one might run into?

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  • ASP.NET MVC DataAnnotations different tables. Can it be done?

    - by mazhar kaunain baig
    i have a language table which is as a foreign key in the link table , The link can be in 3 languages meaning there will be 3 rows in the link table every time i enter the record . i am using jQuery tabs to enter the records in 3 languages . OK so that thing is that there will be three text boxes for every field in the table.link name field will have 3 text boxes, description will have 3 text boxes and so on. i am using LINK to SQL with VS2010. i will be creating link class with MetadataType so how will i handle for eg link name attribute 3 times

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  • How do I search nodes of XML document for text? Or convert to SQL tables?

    - by netefficacy
    Hi I have an XML file and would like to run a search on the nodes for text that matches user input. My options are: Convert the XML file to a SQL table and run the search against the table records. Search the XML nodes themselves. The problem is that I cannot find a open source conversion utility, nor can I figure out how to search the XML nodes. I can use PHP, Ruby, or Python for the search code. Any pointers on how can I do 1 or 2? Thanks

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  • Is it safe to modify CCK tables by hand?

    - by LanguaFlash
    I'm not intimately familiar with CCK but I have a one-time custom setup and know that I could get some performance gains if I created indexes and changed the field type and length of some of the fields in my CCK table. Is it save to modify this table at all or will I end up destroying something in the process? Thanks

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  • How should I set up these tables for searching?

    - by thewebguy
    My PHP site is an online store with about 5k products. Products belong to a vendor, a category, and possibly a subcategory. Each of those items has a name and the products have descriptions. The search queries we've set up work wonderfully, but tend to run pretty slow. They range between 0.20s and 30s (yes 30 seconds). We've optimized like crazy and I'm starting to think we're out of room to improve on that front, so we're caching them and that's making life a lot easier. But when they run they are still killing the server, because what appears to be all of the table locking that comes with MyISAM. So on to my question: Is there a way for us to use InnoDB (row-level locking) and still maintain FULLTEXT? Should we move our DB offsite and use a service like DB2? Is there some other search engine type software we should use instead? Any help is greatly appreciated :)

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  • MYSQL inserting records form table A into tables B and C (linked by foreign key) depending on column values in table A

    - by Chez
    Hi All, Have been searching high and low for a simple solution to a mysql insert problem. The problem is as follows: I am putting together an organisational database consisting of departments and desks. A department may or may not have n number of desks. Both departments and desks have their own table linked by a foreign key in desks to the relevant record in departments (i.e. the pk). I have a temporary table which I use to place all new department data (n records long)...In this table n number of desk records for a department follow the department record directly below. In the TEMP table, if a column department_name has a value,it is a department, if it doesn't it will have a value for the column desk and therefore will be a desk which is related to the above department. As I said there maybe several desk records until you get to the next department record. Ok, so what I want to do is the following: Insert the departments into the departments table and its desks into the desks table , generating a foreign key in the desk record to the relevant departments id. In pseudo-ish code: for each record in TEMP table if Department INSERT the record into Departments get the id of the newly created Department record and store it somewhere else if Desk INSERT the desk into the desks table with the relevant departments id as the foreignkey note once again that all departments desks directly follow the department in the TEMP Table Many Thanks

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  • OpenType Font Parsing for Pleasure and Profit (anyone understand these damn tables?)

    - by mustISignUp
    So, this is mainly for fun, I'm poking around and trying to find my way inside a few fonts and i have a few questions i'd reeally appreciate some help on if anyone has done this kind of stuff. cmap table The fonts i am testing with contain several cmap subtables of different formats. I can read them, but i don't understand which i should be using. ie. what is the strategy for choosing the most appropriate subtable? Does this even make sense? glyf table This is really making my head hurt. I'm going by what is on here. Looking at the second table on that page.. I've got 'n' endPtsOfContours, 'n' instructions and 'n' flags but it is not clear to me if i have the same number of flags as contours (i know how many contours i have). Then, to make matters worse..(fun!) i have an array of xCoords and an array of yCoords. These arrays seem to be of indeterminate length and may contain data of either BYTE or SHORT but we are not going to tell you which.. Thanks to anyone willing to shed some light.

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  • alternative in .Net to building Tables/TR/TD manually?

    - by egrunin
    I've got a pile of code here that looks like this: if (stateTax > 0) { tr = new TableRow(); tbl.Rows.Add(tr); td = new TableCell(); td.CssClass = "stdLabel"; td.Text = "NY State Tax"; tr.Cells.Add(td); td = new TableCell(); td.Text = string.Format("{0:C}", stateTax); td.CssClass = "justRight"; tr.Cells.Add(td); } This is a horrible hash of data and layout, but creating a special class or control every time something like this comes up seems almost as bad. What I usually do is write a helper function, which is concise but ugly: if (stateTax > 0) MakeRow(tbl, "NY State Tax", "stdLabel", string.Format("{0:C}", stateTax), "justRight"); And now I'm thinking: haven't I done this 100 times before? Isn't there a more modern way? Just to be explicit: it's a whole list of miscellaneous labels and values. They don't come from any particular data source, and the rules for when rows should be suppressed vary. This example has only two columns, but I have other places with more.

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  • SQL JOIN with two or more tables as output - most efficient way?

    - by littlegreen
    I have an SQL query that executes a LEFT JOIN on another table, then outputs all results that could be coupled into a designated table. I then have a second SQL query that executes the LEFT JOIN again, then outputs the results that could not be coupled to a designated table. In code, this is something like: INSERT INTO coupledrecords SELECT b.col1, b.col2... s.col1, s.col2... FROM bigtable AS b LEFT JOIN smallertable AS s ON criterium WHERE s.col1 IS NOT NULL INSERT INTO notcoupledrecords SELECT b.col1, b.col2... bigtable AS b LEFT JOIN smallertable AS s ON criterium WHERE s.col1 IS NULL My question: I now have to execute the JOIN two times, in order to achieve what I want. I have a feeling that this is twice as slow as it could be. Is this true, and if yes, is there a way to do it more efficiently?

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  • How to access Oracle system tables from inside of a PL/SQL function or procedure?

    - by mjumbewu
    I am trying to access information from an Oracle meta-data table from within a function. For example (purposefully simplified): CREATE OR REPLACE PROCEDURE MyProcedure IS users_datafile_path VARCHAR2(100); BEGIN SELECT file_name INTO users_datafile_path FROM dba_data_files WHERE tablespace_name='USERS' AND rownum=1; END MyProcedure; / When I try to execute this command in an sqlplus process, I get the following errors: LINE/COL ERROR -------- ----------------------------------------------------------------- 5/5 PL/SQL: SQL Statement ignored 6/12 PL/SQL: ORA-00942: table or view does not exist I know the user has access to the table, because when I execute the following command from the same sqlplus process, it displays the expected information: SELECT file_name FROM dba_data_files WHERE tablespace_name='USERS' AND rownum=1; Which results in: FILE_NAME -------------------------------------------------------------------------------- /usr/lib/oracle/xe/oradata/XE/users.dbf Is there something I need to do differently?

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  • Three customer addresses in one table or in separate tables?

    - by DR
    In my application I have a Customer class and an Address class. The Customer class has three instances of the Address class: customerAddress, deliveryAddress, invoiceAddress. Whats the best way to reflect this structure in a database? The straightforward way would be a customer table and a separate address table. A more denormalized way would be just a customer table with columns for every address (Example for "street": customer_street, delivery_street, invoice_street) What are your experiences with that? Are there any advantages and disadvantages of these approaches?

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  • Is there a way to sync (two way) tables betwen a mysql server and a local MS Access?

    - by Kailen
    Help me figure out a solution to a (not so unique) problem. My research group has gps devices attached to migratory animals. Every once in a while, a research tech will be within range of an animal and will get the chance to download all the logged points. Each individual spits out a single dbf and new locations are just appended to the end (so the file is just cumulative). These data need to be shared among a research group. Everyone else (besides me) wants to use access, so they can make small edits and prefer that interface. They do not like using MySQL. The solution I came up with is: a) The person who downloads the file goes to a web page, enters animal ID into a form, chooses .dbf file and uploads to a mysql database on the server (I still have to write php code to read the dbf and write sql insert statements from it). b) Everyone syncs from their local access database to the server. (This is natively possible from access but very clunky). Is there a tool (preferably open source), that can compare a access table to mysql table and sync the two (both ways)? Alternatively, does anyone have a more elegant solution? The ultimate goal is to allow everyone to have access to the most current data on their computers using their preferred database app.

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  • LINQ to SQL, how to write a method which checks if a row exists when we have multiple tables

    - by Beles
    Hi, I'm trying to write a method in C# which can take as parameter a tabletype, column and a columnvalue and check if the got a row with a with value the method looks like: public object GetRecordFromDatabase(Type tabletype, string columnname, string columnvalue) I'm using LINQ to SQL and need to to this in a generic way so I don't need to write each table I got in the DB. I have been doing this so far for each table, but with more than 70 of these it becomes cumbersome and boring to do. Is there a way to generate the following code dynamically, And swap out the hardcoded tablenames with the values from the parameterlist? In this example I have a table in the DB named tbl_nation, which the DataContext pluralizes to tbl_nations, and I'm checking the column for the value if (DB.tbl_nations.Count(c => c.code.Equals(columnvalue)) == 1) { return DB.tbl_nations.Single(c => c.code.Equals(columnvalue)); }

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  • how to get tables of an access db into a list box using c#?

    - by fathatsme
    hi evry1! i needed to create a form in which i hav to browse and open mdb files --- i did this part usin oprnfile dialogue! private void button1_Click(object sender, EventArgs e) { OpenFileDialog oDlg = new OpenFileDialog(); oDlg.Title = "Select MDB"; oDlg.Filter = "MDB (*.Mdb)|*.mdb"; oDlg.RestoreDirectory = true; string dir = Environment.GetFolderPath(Environment.SpecialFolder.Desktop); oDlg.InitialDirectory = dir; DialogResult result = oDlg.ShowDialog(); if (result == DialogResult.OK) { textBox1.Text = oDlg.FileName.ToString(); } } **this is my code so far!!! now i need to make 3 list boxes!! 1st one to display the table names of the db! 2nd to to display field names when clicked on table name!!! 3rd to display attributes on fiels on clickin on it! v can edit the attribute values and on clickin of save button it should update the database!!! pls help** i'm new to C# so if u could pls help specifically on d doubt i asked it wud b really helpful to me

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  • CD/DVD burn error in ImgBurn and Nero

    - by bobby
    I am getting the errors shown below when I try to burn a CD/DVD on my DVD writer. I am seeing this error for every CD/DVD I try to burn. I am not able to write any CDs or DVDs using ImgBurn. The burn log below is a failed burn in Nero. What could be causing this error? Nero Burning ROM bobby 4C85-200E-4005-0004-0000-7660-0800-35X3-0000-407M-MX37-**** (*) Windows XP 6.1 IA32 WinAspi: - NT-SPTI used Nero Version: 7.11.3. Internal Version: 7, 11, 3, (Nero Express) Recorder: <HL-DT-ST DVDRAM GSA-H12N> Version: UL01 - HA 1 TA 1 - 7.11.3.0 Adapter driver: <IDE> HA 1 Drive buffer : 2048kB Bus Type : default CD-ROM: <ATAPI-CD ROM-DRIVE-52MAX > Version: 52PP - HA 1 TA 0 - 7.11.3.0 Adapter driver: <IDE> HA 1 === Scsi-Device-Map === === CDRom-Device-Map === ATAPI-CD ROM-DRIVE-52MAX F: CdRom0 HL-DT-ST DVDRAM GSA-H12N G: CdRom1 ======================= AutoRun : 1 Excluded drive IDs: WriteBufferSize: 83886080 (0) Byte BUFE : 0 Physical memory : 958MB (981560kB) Free physical memory: 309MB (317024kB) Memory in use : 67 % Uncached PFiles: 0x0 Use Inquiry : 1 Global Bus Type: default (0) Check supported media : Disabled (0) 11.6.2010 CD Image 10:43:02 AM #1 Text 0 File SCSIPTICommands.cpp, Line 450 LockMCN - completed sucessfully for IOCTL_STORAGE_MCN_CONTROL 10:43:02 AM #2 Text 0 File Burncd.cpp, Line 3186 HL-DT-ST DVDRAM GSA-H12N Buffer underrun protection activated 10:43:02 AM #3 Text 0 File Burncd.cpp, Line 3500 Turn on Disc-At-Once, using CD-R/RW media 10:43:02 AM #4 Text 0 File DlgWaitCD.cpp, Line 307 Last possible write address on media: 359848 ( 79:59.73) Last address to be written: 318783 ( 70:52.33) 10:43:02 AM #5 Text 0 File DlgWaitCD.cpp, Line 319 Write in overburning mode: NO (enabled: CD) 10:43:02 AM #6 Text 0 File DlgWaitCD.cpp, Line 2988 Recorder: HL-DT-ST DVDRAM G SA-H12N; CDR co de: 00 97 27 18; O SJ entry from: Pla smon Data systems Ltd. ATIP Data: Special Info [hex] 1: D0 00 A0, 2: 61 1B 12 (LI 97:27.18), 3: 4F 3B 4A ( LO 79:59.74) Additional Info [hex] 1: 00 00 00 (invalid), 2: 00 00 00 (invalid), 3: 00 0 0 00 (invalid) 10:43:02 AM #7 Text 0 File DlgWaitCD.cpp, Line 493 >>> Protocol of DlgWaitCD activities: <<< ========================================= 10:43:02 AM #8 Text 0 File ThreadedTransferInterface.cpp, Line 785 Nero Report 1 Nero Burning ROM Setup items (after recorder preparation) 0: TRM_DATA_MODE1 (2 - CD-ROM Mode 1, Joliet) 2 indices, index0 (150) not provided original disc pos #0 + 318784 (318784) = #318784/70:50.34 not relocatable, disc pos for caching/writing not required/not required -> TRM_DATA_MODE1, 2048, config 0, wanted index0 0 blocks, length 318784 blocks [G: HL-DT-ST DVDRAM GSA-H12N] -------------------------------------------------------------- 10:43:02 AM #9 Text 0 File ThreadedTransferInterface.cpp, Line 986 Prepare [G: HL-DT-ST DVDRAM GSA-H12N] for write in CUE-sheet-DAO DAO infos: ========== MCN: "" TOCType: 0x00; Se ssion Clo sed, disc fixated Tracks 1 to 1: Idx 0 Idx 1 Next T rk 1: TRM_DATA_MODE1, 2048/0x00, FilePos 0 307200 6531768 32, ISRC "" DAO layout: =========== ___Start_|____Track_|_Idx_|_CtrlAdr_|_____Size_|______NWA_|_RecDep__________ -150 | lead-in | 0 | 0x41 | 0 | 0 | 0x00 -150 | 1 | 0 | 0x41 | 0 | 0 | 0x00 0 | 1 | 1 | 0x41 | 318784 | 318784 | 0x00 318784 | lead-out | 1 | 0x41 | 0 | 0 | 0x00 10:43:02 AM #10 Text 0 File SCSIPTICommands.cpp, Line 240 SPTILockVolume - completed successfully for FSCTL_LOCK_VOLUME 10:43:02 AM #11 Text 0 File Burncd.cpp, Line 4286 Caching options: cache CDRom or Network-Yes, small files-Yes (<64KB) 10:43:02 AM #12 Phase 24 File dlgbrnst.cpp, Line 1767 Caching of files started 10:43:02 AM #13 Text 0 File Burncd.cpp, Line 4405 Cache writing successful. 10:43:02 AM #14 Phase 25 File dlgbrnst.cpp, Line 1767 Caching of files completed 10:43:02 AM #15 Phase 36 File dlgbrnst.cpp, Line 1767 Burn process started at 48x (7,200 KB/s) 10:43:02 AM #16 Text 0 File ThreadedTransferInterface.cpp, Line 2733 Verifying disc position of item 0 (not relocatable, no disc pos, no patch infos, orig at #0): write at #0 10:43:02 AM #17 Text 0 File MMC.cpp, Line 17806 StartDAO : CD-Text - Off 10:43:02 AM #18 Text 0 File MMC.cpp, Line 22488 Set BUFE: Buffer underrun protection -> ON 10:43:03 AM #19 Text 0 File MMC.cpp, Line 18034 CueData, Len=32 41 00 00 14 00 00 00 00 41 01 00 10 00 00 00 00 41 01 01 10 00 00 02 00 41 aa 01 14 00 46 34 22 10:43:03 AM #20 Text 0 File ThreadedTransfer.cpp, Line 268 Pipe memory size 83836800 10:43:16 AM #21 Text 0 File Cdrdrv.cpp, Line 1405 10:43:16.806 - G: HL-DT-ST DVDRAM GSA-H12N : Queue again later 10:43:42 AM #22 SPTI -1502 File SCSIPassThrough.cpp, Line 181 CdRom1: SCSIStatus(x02) WinError(0) NeroError(-1502) Sense Key: 0x04 (KEY_HARDWARE_ERROR) Nero Report 2 Nero Burning ROM Sense Code: 0x08 Sense Qual: 0x03 CDB Data: 0x2A 00 00 00 4D 00 00 00 20 00 00 00 Sense Area: 0x70 00 04 00 00 00 00 10 53 29 A1 80 08 03 Buffer x0c7d9a40: Len x10000 0xDC 87 EB 41 6E AC 61 5A 07 B2 DB 78 B5 D4 D9 24 0x8D BC 51 38 46 56 0F EE 16 15 5C 5B E3 B0 10 16 0x14 B1 C3 6E 30 2B C4 78 15 AB D5 92 09 B7 81 23 10:43:42 AM #23 CDR -1502 File Writer.cpp, Line 306 DMA-driver error, CRC error G: HL-DT-ST DVDRAM GSA-H12N 10:43:55 AM #24 Phase 38 File dlgbrnst.cpp, Line 1767 Burn process failed at 48x (7,200 KB/s) 10:43:55 AM #25 Text 0 File SCSIPTICommands.cpp, Line 287 SPTIDismountVolume - completed successfully for FSCTL_DISMOUNT_VOLUME 10:44:01 AM #26 Text 0 File Cdrdrv.cpp, Line 11412 DriveLocker: UnLockVolume completed 10:44:01 AM #27 Text 0 File SCSIPTICommands.cpp, Line 450 UnLockMCN - completed sucessfully for IOCTL_STORAGE_MCN_CONTROL Existing drivers: Registry Keys: HKLM\Software\Microsoft\Windows NT\CurrentVersion\WinLogon Nero Report 3

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  • Inheritance Mapping Strategies with Entity Framework Code First CTP5: Part 3 – Table per Concrete Type (TPC) and Choosing Strategy Guidelines

    - by mortezam
    This is the third (and last) post in a series that explains different approaches to map an inheritance hierarchy with EF Code First. I've described these strategies in previous posts: Part 1 – Table per Hierarchy (TPH) Part 2 – Table per Type (TPT)In today’s blog post I am going to discuss Table per Concrete Type (TPC) which completes the inheritance mapping strategies supported by EF Code First. At the end of this post I will provide some guidelines to choose an inheritance strategy mainly based on what we've learned in this series. TPC and Entity Framework in the Past Table per Concrete type is somehow the simplest approach suggested, yet using TPC with EF is one of those concepts that has not been covered very well so far and I've seen in some resources that it was even discouraged. The reason for that is just because Entity Data Model Designer in VS2010 doesn't support TPC (even though the EF runtime does). That basically means if you are following EF's Database-First or Model-First approaches then configuring TPC requires manually writing XML in the EDMX file which is not considered to be a fun practice. Well, no more. You'll see that with Code First, creating TPC is perfectly possible with fluent API just like other strategies and you don't need to avoid TPC due to the lack of designer support as you would probably do in other EF approaches. Table per Concrete Type (TPC)In Table per Concrete type (aka Table per Concrete class) we use exactly one table for each (nonabstract) class. All properties of a class, including inherited properties, can be mapped to columns of this table, as shown in the following figure: As you can see, the SQL schema is not aware of the inheritance; effectively, we’ve mapped two unrelated tables to a more expressive class structure. If the base class was concrete, then an additional table would be needed to hold instances of that class. I have to emphasize that there is no relationship between the database tables, except for the fact that they share some similar columns. TPC Implementation in Code First Just like the TPT implementation, we need to specify a separate table for each of the subclasses. We also need to tell Code First that we want all of the inherited properties to be mapped as part of this table. In CTP5, there is a new helper method on EntityMappingConfiguration class called MapInheritedProperties that exactly does this for us. Here is the complete object model as well as the fluent API to create a TPC mapping: public abstract class BillingDetail {     public int BillingDetailId { get; set; }     public string Owner { get; set; }     public string Number { get; set; } }          public class BankAccount : BillingDetail {     public string BankName { get; set; }     public string Swift { get; set; } }          public class CreditCard : BillingDetail {     public int CardType { get; set; }     public string ExpiryMonth { get; set; }     public string ExpiryYear { get; set; } }      public class InheritanceMappingContext : DbContext {     public DbSet<BillingDetail> BillingDetails { get; set; }              protected override void OnModelCreating(ModelBuilder modelBuilder)     {         modelBuilder.Entity<BankAccount>().Map(m =>         {             m.MapInheritedProperties();             m.ToTable("BankAccounts");         });         modelBuilder.Entity<CreditCard>().Map(m =>         {             m.MapInheritedProperties();             m.ToTable("CreditCards");         });                 } } The Importance of EntityMappingConfiguration ClassAs a side note, it worth mentioning that EntityMappingConfiguration class turns out to be a key type for inheritance mapping in Code First. Here is an snapshot of this class: namespace System.Data.Entity.ModelConfiguration.Configuration.Mapping {     public class EntityMappingConfiguration<TEntityType> where TEntityType : class     {         public ValueConditionConfiguration Requires(string discriminator);         public void ToTable(string tableName);         public void MapInheritedProperties();     } } As you have seen so far, we used its Requires method to customize TPH. We also used its ToTable method to create a TPT and now we are using its MapInheritedProperties along with ToTable method to create our TPC mapping. TPC Configuration is Not Done Yet!We are not quite done with our TPC configuration and there is more into this story even though the fluent API we saw perfectly created a TPC mapping for us in the database. To see why, let's start working with our object model. For example, the following code creates two new objects of BankAccount and CreditCard types and tries to add them to the database: using (var context = new InheritanceMappingContext()) {     BankAccount bankAccount = new BankAccount();     CreditCard creditCard = new CreditCard() { CardType = 1 };                      context.BillingDetails.Add(bankAccount);     context.BillingDetails.Add(creditCard);     context.SaveChanges(); } Running this code throws an InvalidOperationException with this message: The changes to the database were committed successfully, but an error occurred while updating the object context. The ObjectContext might be in an inconsistent state. Inner exception message: AcceptChanges cannot continue because the object's key values conflict with another object in the ObjectStateManager. Make sure that the key values are unique before calling AcceptChanges. The reason we got this exception is because DbContext.SaveChanges() internally invokes SaveChanges method of its internal ObjectContext. ObjectContext's SaveChanges method on its turn by default calls AcceptAllChanges after it has performed the database modifications. AcceptAllChanges method merely iterates over all entries in ObjectStateManager and invokes AcceptChanges on each of them. Since the entities are in Added state, AcceptChanges method replaces their temporary EntityKey with a regular EntityKey based on the primary key values (i.e. BillingDetailId) that come back from the database and that's where the problem occurs since both the entities have been assigned the same value for their primary key by the database (i.e. on both BillingDetailId = 1) and the problem is that ObjectStateManager cannot track objects of the same type (i.e. BillingDetail) with the same EntityKey value hence it throws. If you take a closer look at the TPC's SQL schema above, you'll see why the database generated the same values for the primary keys: the BillingDetailId column in both BankAccounts and CreditCards table has been marked as identity. How to Solve The Identity Problem in TPC As you saw, using SQL Server’s int identity columns doesn't work very well together with TPC since there will be duplicate entity keys when inserting in subclasses tables with all having the same identity seed. Therefore, to solve this, either a spread seed (where each table has its own initial seed value) will be needed, or a mechanism other than SQL Server’s int identity should be used. Some other RDBMSes have other mechanisms allowing a sequence (identity) to be shared by multiple tables, and something similar can be achieved with GUID keys in SQL Server. While using GUID keys, or int identity keys with different starting seeds will solve the problem but yet another solution would be to completely switch off identity on the primary key property. As a result, we need to take the responsibility of providing unique keys when inserting records to the database. We will go with this solution since it works regardless of which database engine is used. Switching Off Identity in Code First We can switch off identity simply by placing DatabaseGenerated attribute on the primary key property and pass DatabaseGenerationOption.None to its constructor. DatabaseGenerated attribute is a new data annotation which has been added to System.ComponentModel.DataAnnotations namespace in CTP5: public abstract class BillingDetail {     [DatabaseGenerated(DatabaseGenerationOption.None)]     public int BillingDetailId { get; set; }     public string Owner { get; set; }     public string Number { get; set; } } As always, we can achieve the same result by using fluent API, if you prefer that: modelBuilder.Entity<BillingDetail>()             .Property(p => p.BillingDetailId)             .HasDatabaseGenerationOption(DatabaseGenerationOption.None); Working With The Object Model Our TPC mapping is ready and we can try adding new records to the database. But, like I said, now we need to take care of providing unique keys when creating new objects: using (var context = new InheritanceMappingContext()) {     BankAccount bankAccount = new BankAccount()      {          BillingDetailId = 1                          };     CreditCard creditCard = new CreditCard()      {          BillingDetailId = 2,         CardType = 1     };                      context.BillingDetails.Add(bankAccount);     context.BillingDetails.Add(creditCard);     context.SaveChanges(); } Polymorphic Associations with TPC is Problematic The main problem with this approach is that it doesn’t support Polymorphic Associations very well. After all, in the database, associations are represented as foreign key relationships and in TPC, the subclasses are all mapped to different tables so a polymorphic association to their base class (abstract BillingDetail in our example) cannot be represented as a simple foreign key relationship. For example, consider the the domain model we introduced here where User has a polymorphic association with BillingDetail. This would be problematic in our TPC Schema, because if User has a many-to-one relationship with BillingDetail, the Users table would need a single foreign key column, which would have to refer both concrete subclass tables. This isn’t possible with regular foreign key constraints. Schema Evolution with TPC is Complex A further conceptual problem with this mapping strategy is that several different columns, of different tables, share exactly the same semantics. This makes schema evolution more complex. For example, a change to a base class property results in changes to multiple columns. It also makes it much more difficult to implement database integrity constraints that apply to all subclasses. Generated SQLLet's examine SQL output for polymorphic queries in TPC mapping. For example, consider this polymorphic query for all BillingDetails and the resulting SQL statements that being executed in the database: var query = from b in context.BillingDetails select b; Just like the SQL query generated by TPT mapping, the CASE statements that you see in the beginning of the query is merely to ensure columns that are irrelevant for a particular row have NULL values in the returning flattened table. (e.g. BankName for a row that represents a CreditCard type). TPC's SQL Queries are Union Based As you can see in the above screenshot, the first SELECT uses a FROM-clause subquery (which is selected with a red rectangle) to retrieve all instances of BillingDetails from all concrete class tables. The tables are combined with a UNION operator, and a literal (in this case, 0 and 1) is inserted into the intermediate result; (look at the lines highlighted in yellow.) EF reads this to instantiate the correct class given the data from a particular row. A union requires that the queries that are combined, project over the same columns; hence, EF has to pad and fill up nonexistent columns with NULL. This query will really perform well since here we can let the database optimizer find the best execution plan to combine rows from several tables. There is also no Joins involved so it has a better performance than the SQL queries generated by TPT where a Join is required between the base and subclasses tables. Choosing Strategy GuidelinesBefore we get into this discussion, I want to emphasize that there is no one single "best strategy fits all scenarios" exists. As you saw, each of the approaches have their own advantages and drawbacks. Here are some rules of thumb to identify the best strategy in a particular scenario: If you don’t require polymorphic associations or queries, lean toward TPC—in other words, if you never or rarely query for BillingDetails and you have no class that has an association to BillingDetail base class. I recommend TPC (only) for the top level of your class hierarchy, where polymorphism isn’t usually required, and when modification of the base class in the future is unlikely. If you do require polymorphic associations or queries, and subclasses declare relatively few properties (particularly if the main difference between subclasses is in their behavior), lean toward TPH. Your goal is to minimize the number of nullable columns and to convince yourself (and your DBA) that a denormalized schema won’t create problems in the long run. If you do require polymorphic associations or queries, and subclasses declare many properties (subclasses differ mainly by the data they hold), lean toward TPT. Or, depending on the width and depth of your inheritance hierarchy and the possible cost of joins versus unions, use TPC. By default, choose TPH only for simple problems. For more complex cases (or when you’re overruled by a data modeler insisting on the importance of nullability constraints and normalization), you should consider the TPT strategy. But at that point, ask yourself whether it may not be better to remodel inheritance as delegation in the object model (delegation is a way of making composition as powerful for reuse as inheritance). Complex inheritance is often best avoided for all sorts of reasons unrelated to persistence or ORM. EF acts as a buffer between the domain and relational models, but that doesn’t mean you can ignore persistence concerns when designing your classes. SummaryIn this series, we focused on one of the main structural aspect of the object/relational paradigm mismatch which is inheritance and discussed how EF solve this problem as an ORM solution. We learned about the three well-known inheritance mapping strategies and their implementations in EF Code First. Hopefully it gives you a better insight about the mapping of inheritance hierarchies as well as choosing the best strategy for your particular scenario. Happy New Year and Happy Code-Firsting! References ADO.NET team blog Java Persistence with Hibernate book a { color: #5A99FF; } a:visited { color: #5A99FF; } .title { padding-bottom: 5px; font-family: Segoe UI; font-size: 11pt; font-weight: bold; padding-top: 15px; } .code, .typeName { font-family: consolas; } .typeName { color: #2b91af; } .padTop5 { padding-top: 5px; } .padTop10 { padding-top: 10px; } .exception { background-color: #f0f0f0; font-style: italic; padding-bottom: 5px; padding-left: 5px; padding-top: 5px; padding-right: 5px; }

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