I'm trying to figure out an exception, and wondering how the id for an Entity object is generated:
System.Data.Entity.DynamicProxies.TaskInstance_EFB25059687D16F3AB6ABF93C582495406916AC2CC28E7E312CB6B50EC3CF7A5.get_TaskLogs()
TaskInstance is the Entity here. It has the same identifier every time the exception happens. Just wondering how it works underneath.
Somehwere in EF's code base concerning proxy type generation, there is this method ...
// <summary>
// Creates an SHA256 hash of a description of all the metadata relevant to the creation of a proxy type
// for this entity type.
// </summary>
private string BuildEntityTypeHash()
{
using (var sha256HashAlgorithm = MetadataHelper.CreateSHA256HashAlgorithm())
{
var hash = sha256HashAlgorithm.ComputeHash(Encoding.ASCII.GetBytes(BuildEntityTypeDescription()));
// convert num bytes to num hex digits
var builder = new StringBuilder(hash.Length * 2);
foreach (var bite in hash)
{
builder.Append(bite.ToString("X2", CultureInfo.InvariantCulture));
}
return builder.ToString();
}
}
... where BuildEntityTypeDescription() is a method that builds a string from the type's navigation properties, key members etc.
So, basically, the proxy type name is a hashed representation of the type's meta data, so it will always be the same string as long as the type doesn't change.
Related
I'm researching with encrypting an EF 6 db column using db interceptors and custom annotation on the ef entity: https://www.codeguru.com/csharp/soft-deleting-entities-cleanly-using-entity-framework-6-interceptors/
However, the guide's example is using a static string to replace the value prior to inserting to the database. I need the original value to encrypt it and then use the new encrypted value to be inserted to the db but I can't seem to figure out how to get the original value.
public static DbModificationClause UpdateIfMatch(this DbModificationClause clause, string property)
{
var propertyExpression = (DbPropertyExpression)((DbSetClause)clause).Property;
// Get the original value to be inserted to the DB
// Encrypt that value and use it instead
var newEncryptedValue = propertyExpression.GetValue()?
if (propertyExpression.Property.Name == property)
{
return DbExpressionBuilder.SetClause(propertyExpression, DbExpression.FromString(newEncryptedValue));
}
return clause;
}
I'm using Filehelpers to parse a very wide, fixed format file and want to be able to take the resulting object and load it into a DB using EF. I'm getting a missing key error when I try to load the object into the DB and when I try and add an Id I get a Filehelpers error. So it seems like either fix breaks the other. I know I can map a Filehelpers object to a POCO object and load that but I'm dealing with dozens (sometimes hundreds of columns) so I would rather not have to go through that hassle.
I'm also open to other suggestions for parsing a fixed width file and loading the results into a DB. One option of course is to use an ETL tool but I'd rather do this in code.
Thanks!
This is the FileHelpers class:
public class AccountBalanceDetail
{
[FieldHidden]
public int Id; // Added to try and get EF to work
[FieldFixedLength(1)]
public string RecordNuber;
[FieldFixedLength(3)]
public string Branch;
// Additional fields below
}
And this is the method that's processing the file:
public static bool ProcessFile()
{
var dir = Properties.Settings.Default.DataDirectory;
var engine = new MultiRecordEngine(typeof(AccountBalanceHeader), typeof(AccountBalanceDetail), typeof(AccountBalanceTrailer));
engine.RecordSelector = new RecordTypeSelector(CustomSelector);
var fileName = dir + "\\MOCK_ACCTBAL_L1500.txt";
var res = engine.ReadFile(fileName);
foreach (var rec in res)
{
var type = rec.GetType();
if (type.Name == "AccountBalanceHeader") continue;
if (type.Name == "AccountBalanceTrailer") continue;
var data = rec as AccountBalanceDetail; // Throws an error if AccountBalanceDetail.Id has a getter and setter
using (var ctx = new ApplicationDbContext())
{
// Throws an error if there is no valid Id on AccountBalanceDetail
// EntityType 'AccountBalanceDetail' has no key defined. Define the key for this EntityType.
ctx.AccountBalanceDetails.Add(data);
ctx.SaveChanges();
}
//Console.WriteLine(rec.ToString());
}
return true;
}
Entity Framework needs the key to be a property, not a field, so you could try declaring it instead as:
public int Id {get; set;}
I suspect FileHelpers might well be confused by the autogenerated backing field, so you might need to do it long form in order to be able to mark the backing field with the [FieldHidden] attribute, i.e.,
[FieldHidden]
private int _Id;
public int Id
{
get { return _Id; }
set { _Id = value; }
}
However, you are trying to use the same class for two unrelated purposes and this is generally bad design. On the one hand AccountBalanceDetail is the spec for the import format. On the other you are also trying to use it to describe the Entity. Instead you should create separate classes and map between the two with a LINQ function or a library like AutoMapper.
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.)
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)
In my code I get the type of an object (Party object) in a for loop and get the property info of a particular property "firstname". All the objects in the Parties[] collection return the same type so I would like to get the type outside of do while loop only once and still need to be able to get the property "firstname" from the correct party object.
Is it possible to do this way? Thanks for any help.
public List<Party> Parties { get; set; }
PropertyInfo info = null;
i = 1
do
{
foreach (Field field in TotalFields)
{
info = Parties[i - 1].GetType().GetProperty("firstname");
//some other code here
}
i++;
} while (i <= Parties.Count);
When you get the value for a property through a PropertyInfo object, you need to pass an object instance from which to fetch the value. This means that you can reuse the same PropertyInfo instance for several objects, given that they are of the same type as the PropertyInfo was created for:
// Note how we get the PropertyInfo from the Type itself, not an object
// instance of that type.
PropertyInfo propInfo = typeof(YourType).GetProperty("SomeProperty");
foreach (YourType item in SomeList)
{
// this assumes that YourType.SomeProperty is a string, just as an example
string value = (string)propInfo.GetValue(item, null);
// do something sensible with value
}
Your question is tagged as being C# 3, but for completeness it's worth mentioning that this can be made somewhat simpler in C# 4 by using dynamic:
foreach (dynamic item in SomeList)
{
string value = item.SomeProperty;
// do something sensible with value
}