I needed a domain class that held a list of Strings. It seems fairly well-known that GORM can't handle this, so I've worked around it. At first I tried using getters and setters in the domain class, but that caused problems. Then I found on Stack Overflow a way to use afterLoad() and beforeValidate() to rewrite properties as shown below. This has worked well to allow me to turn the List into a String for persistence and back to a List for use in the app.
class Entries {
// persisted to database
String _entry
// exposed to app
List entry
static transients = ['entry'] //don't try to persist the List
def afterLoad() {
// split the String from the database into a List
entry = _entry?.split('\\|')
}
def beforeValidate() {
// join the List into a String for persisting
_entry = entry.join('|')
}
static constraints = {
_entry maxSize:4000
}
}
This works fine programmatically. The only problem is that the Grails scaffolding can't deal with this, even if I try to enter a pipe-delimited string. I understand the reason why is that the scaffolding creates a form field for _entry, so entry is null when it tries to save the object. And beforeValidate() relies on a List of Strings to work.
I tried to get around this in the controller, by setting params.entry = params._entry, prior to the call to new Entries(params). [I recognize that this is not a perfect solution, but this was my first pass at getting the form working.] And then I added a test in beforeValidate() to set entry = _entry if entry was null. Basically:
EntriesController.groovy:
params.entry = params._entry // I added this line
def entriesInstance = new Entries(params)
Entries.groovy:
def beforeValidate() {
if( entry == null ) entry = _entry // I added this line
_entry = entry.join('|')
}
I thought that would allow me to enter pipe-delimited strings into the scaffolded Create Entries form and get something into the database.
To my surprise, though, I found that both entry and _entry were null in beforeValidate(), even though I printed and verified that params contained both keys in the controller. I don't understand why this happens. How did my adding a new key to params result in nulls arriving in the domain class?
The follow-up question is, of course, what's the right way to make the scaffolded Create Entries form accept a pipe-delimited String that makes it into the database?
I needed a domain class that held a list of Strings. It seems fairly well-known that GORM can't handle this, so I've worked around it.
I don't agree with you here
class Xyz {
static hasMany = [entries: String]
}
Should create a seperate table to hold your list of strings (It will actually be a Set). Here are the docs
Related
When you generate grails views, grails looks at your relationships and generates the right html for your form data to be automatically binded to the back end domain. For one to one associations grails creates a drop down list.
However, you might not want to present that property as a drop down list but something more custom (for example a text field with autocomplete). As soon as you do that the value that comes to the controller from that field, comes in as a String and you have to first:
Clear errors
Perform a findBy based on a given param and assign it to the property of the domain
I really want to avoid doing findBys in the controller as much as possible because it seems like I am doing logic/things that should not go there. The controller should delegate to the Service layer. It is not clear to me from the grails documentation how would I do that by using bindData which seems to work really well with String, date, Integer properties etc.. but I do not see how bindData is used for properties that are other domains.
I also really want to avoid passing the params object to the Service layer as it seems less reusable (or maybe not, correct me if I am wrong). I guess that I do not like how it looks semantically. I would prefer the first over the second:
#Transactional
class WithdrawService {
def addWithdraw(Withdraw withdraw) {
//perform business logic here
}
def createWithdraw(Map params){
//perform business logic here
}
}
Let's take the following example:
class Withdraw {
Person person
Date withdrawDate
}
and the parent lookup table
class Person {
String name
String lastName
static constraints = {
}
#Override
public String toString() {
return "$name $lastName"
}
}
In order for the bind to happen automatically without any extra work grails passes in the following request params to automatically bind the one to one:
person.id
a person map with the id.
[person.id:2, person:[id:2], withdrawDate:date.struct, withdrawDate_month:11, create:Create, withdrawDate_year:2015, withdrawDate_day:10, action:save, format:null, controller:withdraw]
What is the best way to go about this?
Pass two hidden fields that look exactly like this: person.id:2, person:[id:2] that get populated as a result of the Ajax call that populates the autocomplete?
In the controller do a Person.findBySomeKnownProperty(params.someKnownValue)
Or any other approach?
Say we have something like the standard Book domain object and bookCategory object. In my controller I want to return a subset of list of books to the view. That subset is not achievable using a find query. When I try to filer the return object, it deletes relationships from the database!
I tried this:
class BookCategory{
String name
static hasMany = [books:Book]
}
class Book{
String title
}
def myController() {
def categories
categories = BookCategory.list()
def user = getCurrentUser()
categories.each { category ->
category.books.removeAll { book ->
!isBookBannedForThisUser(book.title, user)
}
[bookCategories: categories]
}
}
The problem is that it permanently removes these books from the categories for all users from the database!!!
I tried putting the method in a service and using a readonly transaction, but this did not help.
I assume that even if I copy all the categories and books into new list, they will still update the DB as they will still have the book IDs (which I need)
Saving to the database when you dont say save() is very dangerous. is there a way to disable this feature completely?
There is a fundamental flaw in your approach. Do not modify your domain instances if you don't intend to have the changes persisted. Doing so is going to cause you headaches.
Your domain model is suppose to be your system of record. Any changes to it are suppose to be persisted.
If you need to gather up data and manipulate it without having it reflected in your domain model then use a DTO (data transfer object) or similar pattern.
Simply calling .discard() will discard the changes you have made from being persisted when the session automatically flushes.
Instead of working against the framework, and disabling behavior, change your approach to be correct.
So I have a class with a property like this:
public class Foo
{
[Column("GBBRSH")
public static string Gibberish { get; set;}
....
}
For saving data, I have it configured so that the update/insert statements use a custom function:
public static string GetTableColumnName(PropertyInfo property)
{
var type = typeof(ColumnAttribute);
var prop = property.GetCustomAttributes(type, false);
if (propr.Count() > 0)
return ((ColumnAttribute)prop.First()).Name;
return property.Name;
}
This handles fine, but I noticed that when I go to retrieve the data, it isn't actually pulling data back via the function for this particular column. I noticed that the other data present was pulled, but the column in question was the only field with data that didn't retrieve.
1) Is there a way to perhaps use the GetTableColumnName function for the retrieval part of Dapper?
2) Is there a way to force Dapper.NET to throw an exception if a scenario like this happens? I really don't want to have a false sense of security that everything is working as expected when it actually isn't (I get that I'm using mapping that Dapper.NET doesn't use by default, but I do want to set it up in that manner).
edit:
I'm looking in the SqlMapper source of Dapper and found:
private static IEnumerable<T> QueryInternal<T>(params) // my knowledge of generics is limited, but how does this work without a where T : object?
{
...
while (reader.Read())
{
yield return (T)func(reader);
}
...
}
so I learned about two things after finding this. Read up on Func and read up on yield (never used either before). My guess is that I need to pass reader.Read() to another function (that checks against column headers and inserts into objects appropriately) and yield return that?
You could change your select statement to work with aliases like "SELECT [Column("GBBRSH")] AS Gibberish" and provide a mapping between the attribute name and the poco property name.
That way, Dapper would fill the matching properties, since it only requires your POCO's to match the exact name of the column.
I'm saving contacts (email, mobile phone, ICQ, AIM etc.) for people like this:
class Person {
static hasMany = {
contacts: Contact
}
}
class Contact {
String code
ContactType type
}
class ContactType {
String name
}
In my view, I've written some Templates for displaying each contact with a select-box for the contact-type and a textfield for the code, spiced up with some JavaScript for adding and deleting.
My question is: Is there an easy and elegant way to update the data similar to personInstance.properties = params or do I have to read out all the fields, deleting removed, updating changed and adding new ones?
I was looking into this some time ago but never got to refactor our code which handles parameters the old-fashioned way.
According to http://www.grails.org/Controllers+-+Data+Binding you can do something like this
def person = new Person(params['person'])
def contact = new Contact(params['contact'])
def conctactType = new ContactType(params['contactType'])
as long as request params are properly namespaced
person.contact.code
person.contact.type.name
You would still have to find out how to handle one to many. Maybe someone who knows can chip in.
Edit:
Came across this doc which describes how to handle one-to-many. It doesn't appear on the main grails site:
http://svn.codehaus.org/grails/tags/GRAILS_DOCS_1_1/src/guide/6.1.6%20Data%20Binding.gdoc
My Sql Server database has some nullable nvarchar fields, and no nvarchar fields containing empty strings. I want to keep it this way, but the default MVC model binder seems to turn null strings into empty strings.
When a controller retrieves a null nvarchar database field, the null field turns into null string inside the controller, and from there the view renders them, say as blank text boxes. When the page is posted, the default model binder uses these blank text boxes to update the model, and the formerly null strings are changed to empty strings. When the data is updated back to the database, nulls are overwritten with empty strings.
What is the easiest way to get model binding to leave these nulls unchanged?
I know you are probably looking for something more sophisticated, but the default behavior of the ModelBinder is to convert empty form field values into the default value for the datatype of your model object property. String properties become empty, int properties become 0, etc.
You can obviously create a validation scheme that will check for string.empty and convert to null prior to updating the DB. For int form fields you will need to check for 0, and then convert to null.
Here's a hack I used a few months ago before I found the eden of stackoverflow. :) It's a pain, and doesn't scale well, but it works:
Basically, you override the binding inside of a partial linq object. If there's a value you know should always be null (but never legitimately empty) you can do the following. I used this for a string-based user id (SID).
partial void OnSubProcess_Owner_UserChanged()
{
if (string.IsNullOrEmpty(this.SubProcess_Owner_User))
this._SubProcess_Owner_User = null;
}
James
The right answer might be to override the default Model binder to add this functionality yourself.
Maybe you could have a NullValueAttribute that you could apply to string properties to identify the null value. Then make empty string a null value.
I am experiencing the same problem at the moment and will probably resort to this
I'm posting this answer to follow through on this question. After working with it for a while I came to see this problem as part of the general concern of model integrity. For a while I had implemented a solution inside my update stored procedures to catch empty strings and turn them to nulls, along the lines of mikerennick's answer above. Later I wanted also to make sure fields were trimmed and I happened to move the application to NHibernate (and most of the stored procedures went away). In the end I embedded some POCO logic to trim and check for empty strings (from whatever source) in the setters as so:
public MyClass {
private string _name;
public string Name {
get { return _name; }
set { _name = value.TrimToNullIfEmpty(); }
}
}
public static class StringExtensions {
public static string TrimToNullIfEmpty(this string s) {
string temp = (s ?? "").Trim();
return temp.Length == 0 ? null : temp;
}
}