I am somewhat new to LINQ and have a quick question regarding deleting.
Say, for example I have 2 tables, Orders and OrderItems. Using LINQ, I can easily create a new child record by using
order.Items.Add(new OrderItem());
and this will create the child record in the database and update its foreign key to the orderId. This is great, I like it! However when I want to remove a child record
order.Items.Remove(orderItem);
I get an error when I sumbit the changes (because its not actually deleting the child row (order item), just removing the foreign keyId). Is it possible to do this the way I would like to? I don't want to have to create a whole bunch of repositories and if ladders to delete all child rows for a large database.
Thanks in advance.
E
You can achieve that in the DB itself by configuring the Foreign key relationship to delete child records on deletion of the parent's key.
Note that this is transparent to Linq2SQL and it will not be aware of it, so it's best to make sure you do not keep the datacontexts around after that, since the OrderItem objects will still be present.
Set ON DELETE CASCADE for the table in question which will let the SQL Server handle this for you.
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I am new in laravel. In my tutorial video teacher use foreign in migration but,i can create my relationships without it and use just belongTo and hasMany.When i use foreign can not delete one post easily (error is you can not delete because parent foreign has child ......).
my question is my way is good or not? and why?
Thank you all
Your way is good but I think foreign keys are better. Had you not had that foreign key, you would have deleted the post but all that post's children (referred to as orphans because they no longer have a parent) would have stuck around. In order to get around the foreign key error, you would need to first delete all the children for that post, and then delete the post.
The good news is foreign keys can also do this for you so you don't need to worry about keeping track of all the children. When you setup the foreign key, if you add the on delete cascade clause, when deleting the post, the database would automatically remove all of the posts's children for you and deleting a post without first deleting the children would no longer result in an error.
If it's your preference to keep the children around even when the post is deleted, you can use on delete set null instead which would simply set the children's foreign key to null rather than delete the record.
This is all useful for enforcing data integrity (databases should contain only accurate and valid data).
The answer really is not 'is this good practice in Laravel' so much as 'is this good practice for database management'.
There are many articles on the topic as to the good and bad side of using foreign keys. Here is a good explanation on the DBA stack exchange
https://dba.stackexchange.com/questions/168590/not-using-foreign-key-constraints-in-real-practice-is-it-ok
My personal preference is to use them to maintain data integrity. The real power comes in adding cascading deletes to the relationship (if applicable to your design).
It really comes down to how good you want your database to be.The main reasons to use foreign keys in your database are
To prevent actions that would destroy links between your tables
This would prevent the invalid data from being inserted to the foreign key column as it has to point to a existing value
Also defining foreign keys makes your query faster depending on database I don't know the exact milliseconds but if I find it out I will post it.
Well from the laravel point of view the way you do is a better way as this is how one of the main teacher of the Laravel(Jeffrey Way) teaches in the getting started with laravel series.
Foreign Keys are the way to define relationship between tables in your database whereas Laravel belongsTo() or hasMany() is a way to define relationship between tables in Laravel
I am a relative newbie to parse (and IOS) so I hope that this question is legitimate. I am using parse tables as events with entries into the table being all who have joined the event. I want to be able to query my project to see if an event (table name) exists. Is there a way to query the entire project to see if a PF object exists based on the table name? Thanks in advance for any help provided.
If I understand well, you are creating a table by event, you will end up having as many tables as events, which is not what you want. In my opinion, you should be creating a table with all events, then another table with all the persons joining the events. On this second table, you will use a Pointer to the first table. This way, you can query all events in the first table and see if a particular event exists.
Q1.Can LINQ to Entity perform create, update or delete operations on a table without a primary key.??if not then suggest me an alternateQ2.I am not able to use DeleteObject to delete a row from a table (error::missing an assembly). What should i do to use DeleteObject. As an alternate to q2.(delete object) i trieddb.check_master.Remove(checks); (error:: Unable to update the EntitySet 'entitysetName' because it has a DefiningQuery and no element exists in the element to support the current operation)Not able to access any object provided by EF like Attach,DeleteObject...etc. (Using code first with existing database approach)
It would be really convenient to you if you add primary key.
Perhaps otherwise, you'll need to use DataContext.ExecuteCommand().
I have a 1:1 relationship between table 'A' and 'B' in my .DBML. The FK in the database is in place and the .DBML diagram shows an association line between 'A' and 'B'. However, I cannot get the code generator to create a child property in the 'A' entity. All I have is the FK column. In the Association properties, I have ChildProperty set to true. However, the code generator will not create the child property. I have dropped and added the two tables several times.
Anyone have any ideas?
The O/R designer will refuse to create an association property if a primary key is missing on one of the associated tables. Make sure all of your associated tables have a primary key.
Not sure, but I think what you call 1:1 is actually seen by the DBML as 1:* because the list can "have" many of your fk-table, e.g. one empley oyee can have one city, but each city can "have" many employees.
AFAIK a primary key in each table is a prerequisite without which the DBML will not "work". An error is issued when saving it. Your project will compile, but you'll see the errors later. HTH
If I have a Customers table linked to an Orders table, and I want to delete a customer and its corresponding orders, then I can do:
dataContext.Orders.DeleteAllOnSubmit(customer.Orders);
dataContext.Customers.DeleteOnSubmit(customer);
...which is great. However, what if I also have an OrderItems table, and I want to delete the order items for each of the orders deleted?
I can see how I could use DeleteAllOnSubmit to cause the deletion of all the order items for a single order, but how can I do it for all the orders?
You might wish to consider using on delete cascade on the foreign key relationship in the database rather then using LINQ to do it. If you wish to use LINQ then
customer.Orders.ForEach(x => x.OrderItems.ForEach(y=> dataContext.OrderItems.Delete(y));
dataContext.Orders.DeleteAllOnSubmit(customer.Orders);
dataContext.Customers.DeleteOnSubmit(customer);
should do it but I haven't tested it.