Not sure if this is called a lookup table... Here's a screenshot of the schema: http://apoads.com/db-schema.png
What I want to do is join the Ad and MilBase table where the MilBase.BaseID is a given value. In the result, I'd like to be able to access the data like so: ad.MilBase.BaseName, etc...
I just can't seem to wrap my mind around this right now... ;/
Your problem is that your schema has the semantics of a many-to-many relationship between Ad and MilBase and as such the really desired way you would be wanting to do this in LINQ would be ad.Milbases which would then hold a Collection of Milbases.
The problem is not made any better by the fact that LINQ To SQL does not support many-to-many relationships directly, and in reality (assuming that your lookup table only defines a one-to-one or one-to-many relationship) you'd have to do something like
ad.Adbases.Single().MilBase
Of course assuming there will always be one - if that's not the case, then you've got some more complicated things ahead of you.
Of course a join is also always possible too - either way - if this is not the information you were looking for, could you clarify the relationship between Ad and Milbase? (many-to-many, etc?). Also - if this is not a many-to-many and you are able to do so, I would really change this to be a foreign key in either Milbase or the Ad table.
EDIT: In response to your comment,
You could do something like
var query = from a in db.ad
select new {
a.property1,
a.property2,
...
Milbases = a.Adbases.Select(s => s.Milbase)
};
Obviously that code won't compile, but it should give you a rough idea - also I'm certain it can be done in better ways, but something like that should work.
Related
Curious if I constructed and tracked this m2m relationship correctly. Seems strange that every object in those arrays are named "user": {...} or "pip": {...}
Seems like these both should work
Update with screenshots:
Users table relationships:
Pips table relationships:
There's currently no automatic way to "hide" the join table from the GraphQL query and response. You need to traverse through the join table to get back the results you want from both directions so you can't avoid it using the default generated API.
It is possible to extend the GraphQL API using SQL Views if you want to try and "flatten" things from the perspective of people consuming this data.
Alternatively, I'd recommend calling the relationship something different to make it obvious that you're navigating through a join table. I'd recommend actually calling the relationship user_pips instead of pips as it makes it more clear what you're actually retrieving.
I have a Laravel 8 application and am wondering how to solve the problem of how to solve a typical polymorphic issue. I have an Employee model. That Employee can be an ExecutiveEmployee or EntryLevelEmployee. There will be methods an ExecutiveEmployee has that an EntryLevelEmployee doesn't have and the inverse is also true.
Using Laravel 8, is it right to create a base Employee model (without a corresponding table?) and then create two models named ExecutiveEmployee and EntryLevelEmployee that inherit from Employee? This would also imply that both employee types will have two different database tables, even though there will be a lot of overlapping data.
Does it make sense to just have one Employee model and create a migration that has the employee type listed in the model? I am assuming that it's ok if an EntryLevelEmployee has some database attributes which are relevant to it that may or may not be relevant to an ExecutiveEmployee type here, or is that an incorrect assumption?
What's the correct way to model this in Laravel 8? I prefer to keep everything in one table because of how similar the models are. I do have to keep in mind that there will be data that one has that the other doesn't. There will be different accessor methods as well.
Is it possible to have everything in one employees table while utilizing multiple models? Meaning, if I create two models named ExecutiveEmployee and EntryLevelEmployee they would both query the underlying table employees?
UPDATE 1
The more I research, the more I think polymorphism is the incorrect approach here and what I might need is Single-Table Inheritance. This package seems to bring the capability to Eloquent. Would there be a good reason to not use this?
I would use polymorphic relationships in this case, because you are more flexible and have less coupling.
Using the Single Table Inheritance (STI), you can add type specific columns in the employees table and make them nullable. But think about adding/removing types in the future.
executive_employees
id - integer
executive_specific - string
entry_level_employees
id - integer
entry_level_specific - string
employees
id - integer
name - string
email - string
employable_id - integer
employable_type - string
As for the STI the same would be
employees
id - integer
name - string
email - string
type - string
executive_specific - nullable string
entry_level_specific - nullable string
So STI would be suitable when you don't have type specific columns. But you want to add specific behavior in your code. For example a User type (Admin, Author).
Even so, it's a matter of preferences.
It really depends on the state and behavior of your employee object.
Below are few points I will consider to make a decision
If your objects' states/properties are different then definitely you will create different models as your data will be stored in different tables.
If most states/properties are same and some are different, you can
consider storing all in one table/model and for the difference in
behavior create separate table like Ron Van Der Heijden has
suggested and you can consider query scope with that to make
transaction with database.
And another view will be
How many JOINs you will create if you will create different tables,
will that impact the performance and other stuffs, will it make your
code complex?
Can you make simpler relations and handle stuffs independently?
When you are making an API, will your
code make the api overworking? or you need to create too many request
for any operation?
These stuffs will decide how you will make a decision.
Update 1:
Another point I would like to add about the package you are thinking to use, consider using a parent key in table and you can define relationships in a single model.I do not think you need to use a package, you can define it yourself, I guess.
I don't understand why you don't create a simple one-to-many relation. Based on the information you provided, the polymorphic relation looks unnecessary. I think the right way is to create employee_roles table and relations. Then you can give different permissions to different employee types. There are several ways to do that. You can create a middleware to create route restrictions. You can check the role before executing a function in the controller, and run only if the employee has permission. You can use if-else in blade not to render the parts that can't be used by auth user etc.
If you have different “types” of employees, and each employee type should have different logic then yeah, that sounds like a polymorphic relationship.
I am struggling a bit on what probably is a simple matter or something I misunderstand... But anyway, using Linq entity code first, I am trying to keep some of my tables to be inaccessible from the client, without success.
Using Breeze, I have made a datacontext that holds only the dbsets I want exposed, fine.
But when I write a query using .expand(). For example, let's say I have a posts table which I want to expose, and an Owner table that I want to hide.
Using a query like:
var query = EntityQuery
.from('Posts')
.expand('Owner');
I can still see all the columns from Owner.
So the question is: in Linq, how am I supposed to secure/protect/hide the tables, and/or specific columns, that I want to hide?
After some digging, all I have found is the [JsonIgnore] attribute, which seems insufficient to me.
What is the best way to do this? I feel I am missing something probably huge here, but it's the end of the day around here...
Thanks
If you are using the Breeze's WebApi implementation then Breeze also supports ODataQueryOptions ( see here and here ).
This allows you to mark up your controller methods so as to limit how the query is interpreted. For example, to only allow filtering on your 'Posts' query and therefore exclude the ability to "expand" or "select" 'Owners' from any 'Posts' request you could do the following.
[Queryable(AllowedQueryOptions=AllowedQueryOptions.Filter| AllowedQueryOptions.Top | AllowQueryOptions.Skip)]
public IQueryable<Posts> Posts() {
....
}
Ok apparently my question was already addressed here:
Risks of using OData and IQueryable
I just found it.
In the Doctrine manual, under Constrain relationships as much as possible, it gives the advice "Eliminate nonessential associations" and "avoid bidirectional associations if possible". I don't understand what criteria would make an association "essential".
I say this because it seems that you would often want to go from the One side of a One-to-Many association rather than from the Many side. For example, I would want to get all of a User's active PhoneNumbers, rather than get all active PhoneNumbers and their associated User. This becomes more important when you have to traverse multiple One-to-Many relations, e.g. if you wanted to see all Users with a MissedCall from the last two days (MissedCall->PhoneNumber->User).
This is how the simple case would look with an inverse association:
SELECT * FROM User u
LEFT JOIN u.PhoneNumbers p WITH p.active
It would make it more sensible if there were a way to go across a given relation in the opposite direction in DQL, like the following raw SQL:
SELECT * FROM User u
LEFT JOIN PhoneNumber p ON p.User_id = u.id AND p.active
Can someone explain why they give this advice, and in what cases it would be worth ignoring?
-- Edit --
If there are mitigating factors or other workarounds, please give me simple example code or a link.
I do not see any way to traverse a relation's inverse when that inverse is not defined, so I'm going to assume that building custom DQL is not in fact a solution -- there are some joins that are trivial with SQL that are impossible with DQL, and hydration probably wouldn't work anyway. This is why I don't understand why adding inverse relations is a bad idea.
Using Doctrine, I only define relationships when they're needed. This means that all of the relationships defined are actually used in the codebase.
For projects with a large team working on different areas of the project, not everyone will be accustomed to Doctrine, it's current configuration, and eager/lazy loading relationships. If you define bi-directional relationships where they aren't essential and possibly don't make sense, it could potentially lead to extra queries for data that:
may not be used
may have been selected previously
Defining only essential relationships will allow you greater control over how you and your team traverse through your data and reduce extra or overly large queries
Updated 22/08/2011
By essential relationships, I mean the ones you use. It doesn't make sense to define a relationship you wouldn't use. For example:
\Entity\Post has a defined relationship to both \Entity\User and \Entity\Comment
Use $post->user to get author
Use $post->comments to get all comments
\Entity\User has a defined relationship to both \Entity\Post and \Entity\Comment
Use $user->posts to get all user posts
Use $user->comments to get all user comments
\Entity\Comment only has a relationship to \Entity\User
Use $comment->user to get author
Cannot use $comment->post as I don't retrieve the post it belongs to in my application
I wouldn't think of them as "Inverse" relationships. Think of them as "Bi-directional", if using the data in both directions makes sense. If it doesn't make sense, or you wouldn't use the data that way around, don't define it.
I hope this makes sense
I think this is a great question, and am looking forward to others' answers.
Generally, I've interpreted the advice you cited in the down to the following rule of thumb:
If I don't need to access the (inverse) association inside my entity, then I typically make it unidirectional. In your example of users and (missed) calls, I'd probably keep it unidirectional, and let some service class or repository handle putting together custom DQL for the odd occurrence when I needed to get a list of all users with recent missed calls. That's a case I'd consider exceptional -- most of the time, I'm just interested in a particular user's calls, so the unidirectional relationship works (at least until I've got so many records that I feel the need to optimize).
I am working with a few legacy tables that have relationships, but those relationships haven't been explicitly set as primary/foreign keys. I created a .dbml file using "Linq To Sql Classes" and established the proper Case.CaseID = CaseInfo.CaseID association. My resulting class is CasesDataContext.
My Tables (One to many):
Case
------------------
CaseID (int not null)
MetaColumn1 (varchar)
MetaColumn2 (varchar)
MetaColumn3 (varchar)
...
CaseInfo
------------------
CaseInfoID (int)
CaseID (int nulls allowed)
CaseInfoMeta (varchar)
...
I'm new to LinqToSQL and am having trouble doing..
CasesDataContext db = new CasesDataContext();
var Cases = from c in db.Cases
where c.CaseInfo.CaseInfoMeta == "some value"
select c;
(Edit) My problem being that CaseInfo or CaseInfos
is not available as a member of Cases.
I heard from a colleague that I might try ADO.Net Entity Data Model to create my Data Context class, but haven't tried that yet and wanted to see if I'd be wasting my time or should I go another route. Any tips, links, help would be most appreciated.
Go back to the designer and check the relation is set up correctly. Here is one real life example, with BillStateMasters have "CustomerMasters1" property (customers for the state):
Ps. naming is being cleaned up ...
Update 1: You also need to make sure both tables have a primary defined. If the primary key isn't defined on the database (and can't be defined for whatever reason), make sure to define them in the designer. Open the column's properties, and set it as primary key. That said, entity tracking also won't work if you haven't a primary key for the entity, which for deletes means it silently doesn't updates the entity. So, make sure to review all entities and to have them all with a primary key (as I said, if it can't be on the db, then on the designer).
CasesDataContext db = new CasesDataContext();
var Cases = from c in db.Cases
join ci in db.CaseInfo on
ci.ID equals c.InfoID
where ci.CaseInfoMeta == "some value"
select new {CASE=c, INFO=ci};
my "join" linq is a bit rusty, but the above should get close to what you're after.
Is the association set to One to One or One to Many? If you have the association set to One to Many, then what you have is an EntitySet, not an EntityRef and you'll need to use a where clause on the dependent set to get the correct value. I suspect that you want a One to One relationship, which is not the default. Try changing it to One to One and see if you can construct the query.
Note: I'm just guessing because you haven't actually told us what the "trouble" actually is.
Your query looks correct and should return a query result set of Case objects.
So... what's the problem?
(Edit) My problem being that CaseInfo
is not available under Cases... i.e.
c.CaseInfo doesn't exist where I'm
assuming it would be if there were
explicit primary/foreign key
relationships.
What do you mean by "not available"? If you created the association in the designer as you say you did, then the query should generate SQL something along the lines of
SELECT [columns]
FROM Case INNER JOIN CaseInfo
ON Case.CaseID = CaseInfo.CaseID
WHERE CaseInfo.CaseInfoMeta = 'some value'
Have you debugged your linq query to get the SQL generated yet? What does it return?
Couple of things you might want to try:
Check the properties of the association. Make sure that the Parent property was created as Public. It does this by default, but something may have changed.
Since you're not getting CaseInfo on C, try typing it the other direction to see if you get ci.Case with intellisense.
Delete and recreate the association all together.
There's something very basic going wrong if the child members are not showing up. It might be best to delete the dbml and recreate the whole thing.
If all else fails, switch to NHibernate. :)
After a few tests, I'm pretty sure the FK relationships are required in the DB regardless of whatever associations are created in Linq-to-SQL. i.e. if you don't have them explicitly set in the DB, then you will have to do a join manually.
Is this c#? I think you need == instead of = on this line:
where c.CaseInfo.CaseInfoMeta = "some value"
should read
where c.CaseInfo.CaseInfoMeta == "some value"