Re: How to do DDD + AR (repositories)
I appreciate you taking the time to blog your experience with this
topic :)
/Mark
On Jan 27, 3:35 pm, Markus Zywitza markus.zywi...@gmail.com wrote:
ICriteria relates to Specification like ActiveRecord-types to a domain
model. ICriteria may resemble a specification, but it is actually a
query in a fluent API format. If you want to go all the way, then you
need a real specification model that is used to create queries by the
repository.
Also, I blogged about my experiences with AR+DDD. You might find it
useful for your own decision what to do.
http://mortslikeus.blogspot.com/2009/01/active-record-and-ddd.html
-Markus
2009/1/27 Mark Jensen don...@gmail.com:
This would actually been my next question :)
usually I would do the same thing you talk about and encapulate the
quiery, but from what I understand with DDD (not saying that this only
goes for DDD, i have just never heard before I started on DDD), you
are allowed to make this sort methods.
using the Criterion as a parameter for method like the FindOne(),
seems to follow the guideline/rule of the SPECIFICATION Pattern and
thereby add flexiblity to the design.
The argument to us the FindMeSomething(iNeed) and thereby making hard-
coded quires, should be that the client would have done this anyway.
So it makes sense to make hardcoded quires because they give you some
convience
But the issue with FindMeSomething(iNeed), is that the developer need
to understand the inner workings/implications of using a encapsulated
metod... meaning that, if they dont know about how the method quiries
the database, they might pull to much data into memory and thereby
bringing the system down.
you could probably refactor yourself out of this problem, but still...
/Mark
On Jan 26, 3:55 pm, Markus Zywitza markus.zywi...@gmail.com wrote:
Code from the article you linked:
public virtual T FindOne(params ICriterion[] criteria)
{
return ActiveRecordMediatorT.FindOne(criteria);
}
This moves the responsibility for creating a particular query from the
repository to the higher layers, who need to know about an aggregate's
inner workings. Once you start to optimize for n+1 etc., this
knowledge of the persistence is rather deepened than encapsulated.
A better approach is to create a bunch of
FindByWhateverMyAppNeeds(string iNeedThat). That's ugly, but
encapsulates persistence within the repository.
-Markus
2009/1/26 Mark Jensen don...@gmail.com:
Hi Markus
Could you explain the contradictions a bit more for me?
thanks :)
On Jan 26, 1:22 pm, Markus Zywitza markus.zywi...@gmail.com wrote:
You lose nothing with dropping ActiveRecordBase but convenience.
But keep in mind:
1) AR classes without ARBase make good DTOs, but still bad domain
classes.
2) Generic repositories are an antipattern. A repository should
encapsulate the knowledge of an aggregate's persistence details. That
contradicts with ready-to-use-plugs for LINQ or criteria queries.
If you need to do DDD, use AR as DTO and map it to the domain layer.
If you are doing this because DDD has a momentary hype, just don't do
it at all. The Domain Model is not the only enterprise pattern that
yields maintainable software.
-Markus
2009/1/26 Mark Jensen don...@gmail.com:
Hi
From what i can read on the internet people do really like this
combination due to the placement of the persitance logic.
how ever, i know that Castles AR has something callsed
ActiveRecordMediator which seems to be the solution to the problem
above. (i also know ayendes rhino commons which also have an
implementation of the repository pattern).
The questions are.
1. Will i lose something if i stop inheritting from ActiveRecordBase
and use ActiveRecordMediatior instead? (to me it seems like i will get
a lot more functionality/control)
2. Can someone me how to implement the Repository pattern with
ActiveRecordMediator. I have found this example here
http://www.lostechies.com/blogs/johnteague/archive/2008/05/27/using-d...
but to me it seems like I would have to make a Repository (and inherit
from BaseRepository) for every Aggregate and then I need to
instantiate the Repository it when i want to use it.
Is there a better way of doing this?
:)
best regards,
Mark
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Re: How to do DDD + AR (repositories)
This would actually been my next question :)
usually I would do the same thing you talk about and encapulate the
quiery, but from what I understand with DDD (not saying that this only
goes for DDD, i have just never heard before I started on DDD), you
are allowed to make this sort methods.
using the Criterion as a parameter for method like the FindOne(),
seems to follow the guideline/rule of the SPECIFICATION Pattern and
thereby add flexiblity to the design.
The argument to us the FindMeSomething(iNeed) and thereby making hard-
coded quires, should be that the client would have done this anyway.
So it makes sense to make hardcoded quires because they give you some
convience
But the issue with FindMeSomething(iNeed), is that the developer need
to understand the inner workings/implications of using a encapsulated
metod... meaning that, if they dont know about how the method quiries
the database, they might pull to much data into memory and thereby
bringing the system down.
you could probably refactor yourself out of this problem, but still...
/Mark
On Jan 26, 3:55 pm, Markus Zywitza markus.zywi...@gmail.com wrote:
Code from the article you linked:
public virtual T FindOne(params ICriterion[] criteria)
{
return ActiveRecordMediatorT.FindOne(criteria);
}
This moves the responsibility for creating a particular query from the
repository to the higher layers, who need to know about an aggregate's
inner workings. Once you start to optimize for n+1 etc., this
knowledge of the persistence is rather deepened than encapsulated.
A better approach is to create a bunch of
FindByWhateverMyAppNeeds(string iNeedThat). That's ugly, but
encapsulates persistence within the repository.
-Markus
2009/1/26 Mark Jensen don...@gmail.com:
Hi Markus
Could you explain the contradictions a bit more for me?
thanks :)
On Jan 26, 1:22 pm, Markus Zywitza markus.zywi...@gmail.com wrote:
You lose nothing with dropping ActiveRecordBase but convenience.
But keep in mind:
1) AR classes without ARBase make good DTOs, but still bad domain classes.
2) Generic repositories are an antipattern. A repository should
encapsulate the knowledge of an aggregate's persistence details. That
contradicts with ready-to-use-plugs for LINQ or criteria queries.
If you need to do DDD, use AR as DTO and map it to the domain layer.
If you are doing this because DDD has a momentary hype, just don't do
it at all. The Domain Model is not the only enterprise pattern that
yields maintainable software.
-Markus
2009/1/26 Mark Jensen don...@gmail.com:
Hi
From what i can read on the internet people do really like this
combination due to the placement of the persitance logic.
how ever, i know that Castles AR has something callsed
ActiveRecordMediator which seems to be the solution to the problem
above. (i also know ayendes rhino commons which also have an
implementation of the repository pattern).
The questions are.
1. Will i lose something if i stop inheritting from ActiveRecordBase
and use ActiveRecordMediatior instead? (to me it seems like i will get
a lot more functionality/control)
2. Can someone me how to implement the Repository pattern with
ActiveRecordMediator. I have found this example here
http://www.lostechies.com/blogs/johnteague/archive/2008/05/27/using-d...
but to me it seems like I would have to make a Repository (and inherit
from BaseRepository) for every Aggregate and then I need to
instantiate the Repository it when i want to use it.
Is there a better way of doing this?
:)
best regards,
Mark
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Re: How to do DDD + AR (repositories)
ICriteria relates to Specification like ActiveRecord-types to a domain
model. ICriteria may resemble a specification, but it is actually a
query in a fluent API format. If you want to go all the way, then you
need a real specification model that is used to create queries by the
repository.
Also, I blogged about my experiences with AR+DDD. You might find it
useful for your own decision what to do.
http://mortslikeus.blogspot.com/2009/01/active-record-and-ddd.html
-Markus
2009/1/27 Mark Jensen don...@gmail.com:
This would actually been my next question :)
usually I would do the same thing you talk about and encapulate the
quiery, but from what I understand with DDD (not saying that this only
goes for DDD, i have just never heard before I started on DDD), you
are allowed to make this sort methods.
using the Criterion as a parameter for method like the FindOne(),
seems to follow the guideline/rule of the SPECIFICATION Pattern and
thereby add flexiblity to the design.
The argument to us the FindMeSomething(iNeed) and thereby making hard-
coded quires, should be that the client would have done this anyway.
So it makes sense to make hardcoded quires because they give you some
convience
But the issue with FindMeSomething(iNeed), is that the developer need
to understand the inner workings/implications of using a encapsulated
metod... meaning that, if they dont know about how the method quiries
the database, they might pull to much data into memory and thereby
bringing the system down.
you could probably refactor yourself out of this problem, but still...
/Mark
On Jan 26, 3:55 pm, Markus Zywitza markus.zywi...@gmail.com wrote:
Code from the article you linked:
public virtual T FindOne(params ICriterion[] criteria)
{
return ActiveRecordMediatorT.FindOne(criteria);
}
This moves the responsibility for creating a particular query from the
repository to the higher layers, who need to know about an aggregate's
inner workings. Once you start to optimize for n+1 etc., this
knowledge of the persistence is rather deepened than encapsulated.
A better approach is to create a bunch of
FindByWhateverMyAppNeeds(string iNeedThat). That's ugly, but
encapsulates persistence within the repository.
-Markus
2009/1/26 Mark Jensen don...@gmail.com:
Hi Markus
Could you explain the contradictions a bit more for me?
thanks :)
On Jan 26, 1:22 pm, Markus Zywitza markus.zywi...@gmail.com wrote:
You lose nothing with dropping ActiveRecordBase but convenience.
But keep in mind:
1) AR classes without ARBase make good DTOs, but still bad domain classes.
2) Generic repositories are an antipattern. A repository should
encapsulate the knowledge of an aggregate's persistence details. That
contradicts with ready-to-use-plugs for LINQ or criteria queries.
If you need to do DDD, use AR as DTO and map it to the domain layer.
If you are doing this because DDD has a momentary hype, just don't do
it at all. The Domain Model is not the only enterprise pattern that
yields maintainable software.
-Markus
2009/1/26 Mark Jensen don...@gmail.com:
Hi
From what i can read on the internet people do really like this
combination due to the placement of the persitance logic.
how ever, i know that Castles AR has something callsed
ActiveRecordMediator which seems to be the solution to the problem
above. (i also know ayendes rhino commons which also have an
implementation of the repository pattern).
The questions are.
1. Will i lose something if i stop inheritting from ActiveRecordBase
and use ActiveRecordMediatior instead? (to me it seems like i will get
a lot more functionality/control)
2. Can someone me how to implement the Repository pattern with
ActiveRecordMediator. I have found this example here
http://www.lostechies.com/blogs/johnteague/archive/2008/05/27/using-d...
but to me it seems like I would have to make a Repository (and inherit
from BaseRepository) for every Aggregate and then I need to
instantiate the Repository it when i want to use it.
Is there a better way of doing this?
:)
best regards,
Mark
--~--~-~--~~~---~--~~
You received this message because you are subscribed to the Google Groups
Castle Project Users group.
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Re: How to do DDD + AR (repositories)
Well you wouldn't necessarily have to make a repo for every entity because you'd have a generic RepoT you could use. However you might create (as an example) a UserRepo : BaseRepoUser with a FindByUsername method as a little syntactic sugar. I think many people would use a container such as windsor to avoid having to manually instantiate their repositories. On Mon, Jan 26, 2009 at 11:02 AM, Mark Jensen don...@gmail.com wrote: Hi From what i can read on the internet people do really like this combination due to the placement of the persitance logic. how ever, i know that Castles AR has something callsed ActiveRecordMediator which seems to be the solution to the problem above. (i also know ayendes rhino commons which also have an implementation of the repository pattern). The questions are. 1. Will i lose something if i stop inheritting from ActiveRecordBase and use ActiveRecordMediatior instead? (to me it seems like i will get a lot more functionality/control) 2. Can someone me how to implement the Repository pattern with ActiveRecordMediator. I have found this example here http://www.lostechies.com/blogs/johnteague/archive/2008/05/27/using-database-repository-pattern-with-activerecord-with-activerecordmediator.aspx but to me it seems like I would have to make a Repository (and inherit from BaseRepository) for every Aggregate and then I need to instantiate the Repository it when i want to use it. Is there a better way of doing this? :) best regards, Mark --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Castle Project Users group. To post to this group, send email to castle-project-users@googlegroups.com To unsubscribe from this group, send email to castle-project-users+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/castle-project-users?hl=en -~--~~~~--~~--~--~---
Re: How to do DDD + AR (repositories)
You lose nothing with dropping ActiveRecordBase but convenience. But keep in mind: 1) AR classes without ARBase make good DTOs, but still bad domain classes. 2) Generic repositories are an antipattern. A repository should encapsulate the knowledge of an aggregate's persistence details. That contradicts with ready-to-use-plugs for LINQ or criteria queries. If you need to do DDD, use AR as DTO and map it to the domain layer. If you are doing this because DDD has a momentary hype, just don't do it at all. The Domain Model is not the only enterprise pattern that yields maintainable software. -Markus 2009/1/26 Mark Jensen don...@gmail.com: Hi From what i can read on the internet people do really like this combination due to the placement of the persitance logic. how ever, i know that Castles AR has something callsed ActiveRecordMediator which seems to be the solution to the problem above. (i also know ayendes rhino commons which also have an implementation of the repository pattern). The questions are. 1. Will i lose something if i stop inheritting from ActiveRecordBase and use ActiveRecordMediatior instead? (to me it seems like i will get a lot more functionality/control) 2. Can someone me how to implement the Repository pattern with ActiveRecordMediator. I have found this example here http://www.lostechies.com/blogs/johnteague/archive/2008/05/27/using-database-repository-pattern-with-activerecord-with-activerecordmediator.aspx but to me it seems like I would have to make a Repository (and inherit from BaseRepository) for every Aggregate and then I need to instantiate the Repository it when i want to use it. Is there a better way of doing this? :) best regards, Mark --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Castle Project Users group. To post to this group, send email to castle-project-users@googlegroups.com To unsubscribe from this group, send email to castle-project-users+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/castle-project-users?hl=en -~--~~~~--~~--~--~---
Re: How to do DDD + AR (repositories)
This cries for at least to mention those other patterns. On Mon, Jan 26, 2009 at 3:22 PM, Markus Zywitza markus.zywi...@gmail.comwrote: The Domain Model is not the only enterprise pattern that yields maintainable software. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Castle Project Users group. To post to this group, send email to castle-project-users@googlegroups.com To unsubscribe from this group, send email to castle-project-users+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/castle-project-users?hl=en -~--~~~~--~~--~--~---
Re: How to do DDD + AR (repositories)
:) so you would also do something like the example from the link shows, but just remove the FindAll ? On Jan 26, 12:20 pm, Ken Egozi egoz...@gmail.com wrote: my take: externally the domain API will expose specialised repositories for aggregate roots. (not all of them should have Save, and a generic FindAll is not informative imo) internally, in the repository implementations, they'd use ARMediator (or NH queries) to retrieve manipulate data On Mon, Jan 26, 2009 at 1:08 PM, Colin Ramsay colinram...@gmail.com wrote: Well you wouldn't necessarily have to make a repo for every entity because you'd have a generic RepoT you could use. However you might create (as an example) a UserRepo : BaseRepoUser with a FindByUsername method as a little syntactic sugar. I think many people would use a container such as windsor to avoid having to manually instantiate their repositories. On Mon, Jan 26, 2009 at 11:02 AM, Mark Jensen don...@gmail.com wrote: Hi From what i can read on the internet people do really like this combination due to the placement of the persitance logic. how ever, i know that Castles AR has something callsed ActiveRecordMediator which seems to be the solution to the problem above. (i also know ayendes rhino commons which also have an implementation of the repository pattern). The questions are. 1. Will i lose something if i stop inheritting from ActiveRecordBase and use ActiveRecordMediatior instead? (to me it seems like i will get a lot more functionality/control) 2. Can someone me how to implement the Repository pattern with ActiveRecordMediator. I have found this example here http://www.lostechies.com/blogs/johnteague/archive/2008/05/27/using-d... but to me it seems like I would have to make a Repository (and inherit from BaseRepository) for every Aggregate and then I need to instantiate the Repository it when i want to use it. Is there a better way of doing this? :) best regards, Mark -- Ken Egozi.http://www.kenegozi.com/bloghttp://www.delver.comhttp://www.musicglue.comhttp://www.castleproject.orghttp://www.gotfriends.co.il --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Castle Project Users group. To post to this group, send email to castle-project-users@googlegroups.com To unsubscribe from this group, send email to castle-project-users+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/castle-project-users?hl=en -~--~~~~--~~--~--~---
Re: How to do DDD + AR (repositories)
Hi Markus Could you explain the contradictions a bit more for me? thanks :) On Jan 26, 1:22 pm, Markus Zywitza markus.zywi...@gmail.com wrote: You lose nothing with dropping ActiveRecordBase but convenience. But keep in mind: 1) AR classes without ARBase make good DTOs, but still bad domain classes. 2) Generic repositories are an antipattern. A repository should encapsulate the knowledge of an aggregate's persistence details. That contradicts with ready-to-use-plugs for LINQ or criteria queries. If you need to do DDD, use AR as DTO and map it to the domain layer. If you are doing this because DDD has a momentary hype, just don't do it at all. The Domain Model is not the only enterprise pattern that yields maintainable software. -Markus 2009/1/26 Mark Jensen don...@gmail.com: Hi From what i can read on the internet people do really like this combination due to the placement of the persitance logic. how ever, i know that Castles AR has something callsed ActiveRecordMediator which seems to be the solution to the problem above. (i also know ayendes rhino commons which also have an implementation of the repository pattern). The questions are. 1. Will i lose something if i stop inheritting from ActiveRecordBase and use ActiveRecordMediatior instead? (to me it seems like i will get a lot more functionality/control) 2. Can someone me how to implement the Repository pattern with ActiveRecordMediator. I have found this example here http://www.lostechies.com/blogs/johnteague/archive/2008/05/27/using-d... but to me it seems like I would have to make a Repository (and inherit from BaseRepository) for every Aggregate and then I need to instantiate the Repository it when i want to use it. Is there a better way of doing this? :) best regards, Mark --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Castle Project Users group. To post to this group, send email to castle-project-users@googlegroups.com To unsubscribe from this group, send email to castle-project-users+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/castle-project-users?hl=en -~--~~~~--~~--~--~---
Re: How to do DDD + AR (repositories)
Code from the article you linked:
public virtual T FindOne(params ICriterion[] criteria)
{
return ActiveRecordMediatorT.FindOne(criteria);
}
This moves the responsibility for creating a particular query from the
repository to the higher layers, who need to know about an aggregate's
inner workings. Once you start to optimize for n+1 etc., this
knowledge of the persistence is rather deepened than encapsulated.
A better approach is to create a bunch of
FindByWhateverMyAppNeeds(string iNeedThat). That's ugly, but
encapsulates persistence within the repository.
-Markus
2009/1/26 Mark Jensen don...@gmail.com:
Hi Markus
Could you explain the contradictions a bit more for me?
thanks :)
On Jan 26, 1:22 pm, Markus Zywitza markus.zywi...@gmail.com wrote:
You lose nothing with dropping ActiveRecordBase but convenience.
But keep in mind:
1) AR classes without ARBase make good DTOs, but still bad domain classes.
2) Generic repositories are an antipattern. A repository should
encapsulate the knowledge of an aggregate's persistence details. That
contradicts with ready-to-use-plugs for LINQ or criteria queries.
If you need to do DDD, use AR as DTO and map it to the domain layer.
If you are doing this because DDD has a momentary hype, just don't do
it at all. The Domain Model is not the only enterprise pattern that
yields maintainable software.
-Markus
2009/1/26 Mark Jensen don...@gmail.com:
Hi
From what i can read on the internet people do really like this
combination due to the placement of the persitance logic.
how ever, i know that Castles AR has something callsed
ActiveRecordMediator which seems to be the solution to the problem
above. (i also know ayendes rhino commons which also have an
implementation of the repository pattern).
The questions are.
1. Will i lose something if i stop inheritting from ActiveRecordBase
and use ActiveRecordMediatior instead? (to me it seems like i will get
a lot more functionality/control)
2. Can someone me how to implement the Repository pattern with
ActiveRecordMediator. I have found this example here
http://www.lostechies.com/blogs/johnteague/archive/2008/05/27/using-d...
but to me it seems like I would have to make a Repository (and inherit
from BaseRepository) for every Aggregate and then I need to
instantiate the Repository it when i want to use it.
Is there a better way of doing this?
:)
best regards,
Mark
--~--~-~--~~~---~--~~
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Castle Project Users group.
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