I've created an EDMX object from a database I'm programming against.
I need to get input from a user and save it to a row in the database table. The problem is that I need to limit the length of input strings to the width of the corresponding VARCHAR column in the database.
When I browse the model, I can clearly see in the properties window that the model knows the max length of the string, but I don't know how to access this data in code.
If I want to write something like this:
Entities entities = new Entities();
myTable = entities.myTable.First();
if (userInput.length > myTable.columnA.MaxLength)
{
// tell the user that the input is too long.
}
else
{
myTable.columnA = userInput;
}
How do I write it?
Update: I would like to point out that the IObjectContextAdapater mentioned in the answers below is in the System.Data.Entity.Infrastructure namespace.
Here are two methods by which you can read the meta data:
int? GetMaxLength(DbContext context, string tableName, string propertyName)
{
var oc = ((IObjectContextAdapter)context).ObjectContext;
return oc.MetadataWorkspace.GetItems(DataSpace.CSpace).OfType<EntityType>()
.Where(et => et.Name == tableName)
.SelectMany(et => et.Properties.Where(p => p.Name == propertyName))
.Select (p => p.MaxLength)
.FirstOrDefault();
}
int? GetMaxLength<T>(DbContext context, Expression<Func<T, object>> property)
{
var memberExpression = (MemberExpression)property.Body;
string propertyName = memberExpression.Member.Name;
return GetMaxLength(context, typeof(T).Name, propertyName);
}
So you can either enter the table name and property name, or an expression that specifies the property you're interested in.
Another approach could be to create a MetaData class and use the MaxLength attribute.
It's not very pretty; reading edmx properties at runtime is not something Microsoft exposed easily or documented well (or in some cases, at all). context is your DBContext.
var objectContext = ((IObjectContextAdapter)context).ObjectContext;
var entityType = objectContext.MetadataWorkspace.GetItems<EntityType>(DataSpace.CSpace).Where(e => e.Name == "your entity name").First();
var facets = entityType.Properties["your property name"].TypeUsage.Facets;
facets will look something like this, so you'll need to look for the MaxLength Name(may not exist, depending on the underlying field type) and get the Value:
Count = 5
[0]: Nullable=false
[1]: DefaultValue=null
[2]: MaxLength=250
[3]: Unicode=false
[4]: FixedLength=false
If you modify the T4 template you can add your own attribute to the properties that have MaxLength set.
If you can find the right place to add it, it's something as simple as this:
var lengthAttributeText = edmProperty.MaxLength.HasValue
? string.Format("[MaxLength({0})] ", edmProperty.MaxLength.Value)
: "";
And then add this into the text for the property line. (Tricky to be more detailed since I've already modified my .tt file a lot; also the lack of proper IDE support for .tt files makes this a lot harder than it could be.)
Related
I was told to use automapper in the code below. I cannot get clarification for reasons that are too lengthy to go into. What object am I supposed to be mapping to what object? I don't see a "source" object, since the source is the database...
Would really appreciate any help on how to do this with automapper. Note, the actual fields are irrelevant, I need help with the general concept. I do understand how mapping works when mapping from one object to another.
public IQueryable<Object> ReturnDetailedSummaries(long orgId)
{
var summaries = from s in db.ReportSummaries
where s.OrganizationId == orgId
select new SummaryViewModel
{
Id = s.Id,
Name = s.Name,
AuditLocationId = s.AuditLocationId,
AuditLocationName = s.Location.Name,
CreatedOn = s.CreatedOn,
CreatedById = s.CreatedById,
CreatedByName = s.User.Name,
OfficeId = s.OfficeId,
OfficeName = s.Office.Name,
OrganizationId = s.OrganizationId,
OrganizationName = s.Organization.Name,
IsCompleted = s.IsCompleted,
isHidden = s.isHidden,
numberOfItemsInAuditLocations = s.numberOfItemsInAuditLocations,
numberOfLocationsScanned = s.numberOfLocationsScanned,
numberOfItemsScanned = s.numberOfItemsScanned,
numberofDiscrepanciesFound = s.numberofDiscrepanciesFound
};
return summaries;
}
It is a handy and a timesaver, especially if you use a one to one naming between translations layers. Here is how I use it.
For single item
public Domain.Data.User GetUserByUserName(string userName)
{
Mapper.CreateMap<User, Domain.Data.User>();
return (
from s in _dataContext.Users
where s.UserName==userName
select Mapper.Map<User, Domain.Data.User>(s)
).SingleOrDefault();
}
Multiple Items
public List<Domain.Data.User> GetUsersByProvider(int providerID)
{
Mapper.CreateMap<User, Domain.Data.User>();
return (
from s in _dataContext.Users
where s.ProviderID== providerID
select Mapper.Map<User, Domain.Data.User>(s)
).ToList();
}
It looks like you already have a model? SummaryViewModel?
If this isn't the DTO, then presumably you want to do:
Mapper.CreateMap<SummaryViewModel, SummaryViewModelDto>();
SummaryViewModelDto summaryViewModelDto =
Mapper.Map<SummaryViewModel, SummaryViewModelDto>(summaryViewModel);
AutoMapper will copy fields from one object to another, to save you having to do it all manually.
See https://github.com/AutoMapper/AutoMapper/wiki/Getting-started
The source is your entity class ReportSummary, the target is SummaryViewModel:
Mapper.CreateMap<ReportSummary, SummaryViewModel>();
The best way to use AutoMapper in combination with an IQueryable data source is through the Project.To API:
var summaries = db.ReportSummaries.Where(s => s.OrganizationId == orgId)
.Project().To<SummaryViewModel>();
Project.To translates the properties in the target model straight to the selected columns in the generated SQL.
Mapper.Map, on the other hand, only works on in-memory collections, so you can only use it when you first fetch complete ReportSummary objects from the database. (In this case there may not be much of a difference, but in other cases it can be substantial).
How can I include a related entity, but only select the top 1?
public EntityFramework.Member Get(string userName)
{
var query = from member in context.Members
.Include(member => member.Renewals)
where member.UserName == userName
select member;
return query.SingleOrDefault();
}
According to MSDN:
"Note that it is not currently possible to filter which related entities are loaded. Include will always bring in all related entities."
http://msdn.microsoft.com/en-us/data/jj574232
There is also a uservoice item for this functionality:
http://data.uservoice.com/forums/72025-entity-framework-feature-suggestions/suggestions/1015345-allow-filtering-for-include-extension-method
The approach to use an anonymous object works, even though it's not clean as you wish it would be:
public Member GetMember(string username)
{
var result = (from m in db.Members
where m.Username == username
select new
{
Member = m,
FirstRenewal = m.Renewals.FirstOrDefault()
}).AsEnumerable().Select(r => r.Member).FirstOrDefault();
return result;
}
The FirstRenewal property is used just to make EF6 load the first renewal into the Member object. As a result the Member returned from the GetMember() method contains only the first renewal.
This code generates a single Query to the DB, so maybe it's good enough for You.
I am developing one application in which data is access from edmx entities and from that we have to fill each business entity after retriving data from edmx entity like:-
var tblproducts = tblproductsData
.Select(t => new tblProduct()
{
CategoryID = t.CategoryID,
Description = t.Description,
ID = t.ID,
Image = t.Image,
InsDt = t.InsDt,
Price = t.Price,
Quantity = t.Quantity,
Status = t.Status,
Title = t.Title,
tblCategory = new EFDbFirst.Models.tblCategory()
{
ID = t.tblCategory.ID,
status = t.tblStatus.StatusID,
Title_Category = t.tblCategory.Title_Category
},
tblStatu = new EFDbFirst.Models.tblStatu()
{
StatusDescription = t.tblStatus.StatusDescription
,
StatusID = t.tblStatus.StatusID
}
});
I am fadeup with this because everytime i have to convert one to another while getting data and setting data in db,
Is there any good way to create some common mehod which takes one anonymous type and converts it to another anonymous type.
Thanks in Advance
Your example isn't that clear.
First of all, EF doesn't work with anonymous types inside itself, it works with the EF types you have defined either using edmx file or code first. You can however create anonymous types yourself by defining an Select statement.
E.g:
var products = context.tblProductsData
.Select(r => new { Description = r.Description }); //new without typename is an
//anonymous object
The tblProduct, tblCategory and tblStatu objects, are they EF types? If so, you don't need to write a Select, EF will generate objects for you when you execute it.
E.g:
var products = context.tblProductsData.ToList();
This will automatically generate tblProduct objects for you. When you try to navigate to tblProduct.tblCategory or tblProduct.tblStatu, lazy loading will retrieve them for you. If you want to explicit load them during first query (eager-loading) use the Include function.
E.g:
var products = context.tblProductsData.Include(r => r.tblCategory)
.Include(r => r.tblStatu).ToList();
However if tblProducts, tblCategory and tblStatu is business objects and NOT EF types, there isn't any other way to do this, you have to explicit create them in a Select statement.
I've got a model defined like the following...
#MongoEntity
public class Ent extends MongoModel{
public Hashtable<Integer, CustomType> fil;
public int ID;
public Ent(){
fil = new Hashtable<Integer, CustomType>();
}
}
CustomType is a datatype I've created which basically holds a list of items (among other things). At some point in my web application I update the hashtable from a controller and then read back the size of the item I just updated. Like the following...
public static void addToHash(CustomType type, int ID, int key){
//First I add an element to the list I'm storing in custom type.
Ent ent = Ent.find("byID",ID).first();
CustomType element = user.fil.get(key);
if(element == null) element = new CustomType();
element.add(type);
ent.save();
//Next I reset the variables and read back the value I just stored..
ent = null;
ent = User.find("byID",ID).first();
element = ent.fil.get(ID);
System.out.println("SIZE = " + element.size()); //null pointer here
}
As you can see by my above example I add the element, save the model and then attempt to read back what I have just added and it has not been saved. The above model Ent is a minimal version of the entire Model I'm actually using. All other values in the model including List's, String's, Integer's etc. update correctly when they're updated but this Hashtable I'm storing isn't. Why would this be happening and how could I correct it?
You should probably post on the play framework forum for better help..
Alternatives for a mongodb framework are morphia and springdata which have good documentation.
Not sure how Play maps a hash table to a document value, but it seems it cannot update just the hash table using a mongo operator.
You should be able to mark the whole document for update which would work but slower.
In my domain, there's no important distinction between NULL and an empty string. How do I get EF to ignore the difference between the two and always persist an empty string as NULL?
Empty string is not default value for string property so it means your code is setting empty strings somewhere. In such case it is your responsibility to handle it.
If you are using code first with POCOs you can use custom setter:
private string _myProperty;
public string MyProperty
{
get { return _myProperty; }
set
{
if (value == String.Empty)
{
_myProperty = null;
}
else
{
_myProperty = value;
}
}
}
Here is a function I placed in my DbContext subclass that replaces empty or whitespace strings with null.
I still didn't optimize it so any performance hints will be very appreciated.
private const string StringType = "String";
private const EntityState SavingState = EntityState.Added | EntityState.Modified;
public override int SaveChanges()
{
var objectContext = ((IObjectContextAdapter)this).ObjectContext;
var savingEntries =
objectContext.ObjectStateManager.GetObjectStateEntries(SavingState);
foreach (var entry in savingEntries)
{
var curValues = entry.CurrentValues;
var fieldMetadata = curValues.DataRecordInfo.FieldMetadata;
var stringFields = fieldMetadata.Where(f =>
f.FieldType.TypeUsage.EdmType.Name == StringType);
foreach (var stringField in stringFields)
{
var ordinal = stringField.Ordinal;
var curValue = curValues[ordinal] as string;
if (curValue != null && curValue.All(char.IsWhiteSpace))
curValues.SetValue(ordinal, null);
}
}
return base.SaveChanges();
}
Optimization considerations:
Identify a string type property by different way other than string comparison I tried to look-up some enumeration of the built-in types but didn't find
Cache string fields for types (maybe is unnecessary, will have to decompile and see what the original impl does
Order result by entity type, backup iterated entity type, if next iterated entity is same type, use previous metadata, again, if the metadata is anyway there, performance is cheaper the way it is
Limit string length for whitespace check - i.e. if a string length > x, skip checking whether its a whitespace string or not
I'm using Silverlight and the TextBoxes in the UI set all the string properties to empty strings.
I tried setting:
<TextBox
Text="{Binding MyStringProperty,
Mode=TwoWay,
ValidatesOnDataErrors=True,
TargetNullValue=''}"/>
But it didn't help much.
That's not Entity Framework's job.
You should do it in your repository, or in the database with triggers.
Or do it at the start (e.g when the data comes in, UI, external source, etc)