I'm using EF 5.0 and Code First. In my generic repository I have a method for exclude records in a logical way. This method actually perform a update, setting the status of the entity field to false.
I would like to intercept my queries, and filter only where status == true.
Is there a easy way to do that? Ex:
new GenericRepository<Entity>().ToList();
// and internally it will filter where status == true.
create a generic method
public IQueryable<T> All<T>(Expression<Func<T, bool>> predicate) {
return context.Set<T>().Where(predicate);
}
and if you want something more linked to your status property, you have to use reflection and build the Lambda by yourself (as you can't use interfaces with linq to entites queries).
Something like that (untested), calling the generic All method.
public IQueryable<T>AllButDeleted<T>() {
var property = typeof(T).GetProperty("status");
//check if T has a "status" property
if (property == null && || property.PropertyType != typeof(bool)) throw new ArgumentException("This entity doesn't have an status property, or it's not a boolean");
//build the expression
//m =>
var parameter = new ParameterExpression(typeof(T), "m");
// m.status
Expression body = Expression.Property(parameter, property);
//m.status == true (which is just m.status)
body = Expression.IsTrue(body);
//m => m.status
var lambdaPredicate = Expression.Lambda<Func<T, bool>>(body, new[]{parameter});
return All(lambdaPredicate);
}
You can make all your entities implement some IDeletable interface:
public interface IDelitable
{
bool IsDeleted { get; }
}
And add constraint to generic parameter of your repository
public class GenericRepository<T>
where T: class, IDelitable
And add filter when you are returning values:
context.Set<T>().Where(e => !e.IsDeleted)
You can filter it using Where.
.Where(e => e.Status == true).ToList();
Related
ASP .NET 5 MVC Core application.
Following method is used to find entity by key:
class MyStudents: Students { }
public TEntity FindNormalized<TEntity>(params object[] keyValues)
where TEntity : class
{
return Find<TEntity>(keyValues);
}
void FindNormalized<TEntity>(TEntity entity, params object[] keyValues)
where TEntity : class
{
var res = FindNormalized<TEntity>(keyValues);
if (res == null)
throw new KeyNotFoundException(entity.GetType().Name + " entity key not found " + keyValues[0]);
CopyPropertiesTo(res, entity);
}
static void CopyPropertiesTo<T, TU>(T source, TU dest)
{ // https://stackoverflow.com/questions/3445784/copy-the-property-values-to-another-object-with-c-sharp
var sourceProps = typeof(T).GetProperties().Where(x => x.CanRead).ToList();
var destProps = typeof(TU).GetProperties()
.Where(x => x.CanWrite)
.ToList();
foreach (var sourceProp in sourceProps)
if (destProps.Any(x => x.Name == sourceProp.Name))
{
var p = destProps.First(x => x.Name == sourceProp.Name);
p.SetValue(dest, sourceProp.GetValue(source, null), null);
}
}
Using it with subclass
FindNormalized<MyStudents>(1);
throws exception
Cannot create a DbSet for 'MyStudents' because this type is not
included in the model for the context.
FindNormalized<Students>(1);
works.
How to fix this so that it can used with subclass type also ?
For getting table attribute from subclass code from Dynamic Linq works:
string GetTableAttrib(Type t)
{
foreach (Type t2 in SelfAndBaseClasses(t))
{
IEntityType entityType = Model.FindEntityType(t2);
if (entityType == null)
continue;
return entityType.GetTableName();
}
throw new ApplicationException(t.FullName + " no table attribute");
}
/// <summary>
/// Enumerate inheritance chain - copied from DynamicLinq
/// </summary>
static IEnumerable<Type> SelfAndBaseClasses(Type type)
{
while (type != null)
{
yield return type;
type = type.BaseType;
}
}
Maybe this can used to implement Find also. Unfortunately Find throws exception. Is it reasonable to wrap Find using try/catch or is there better way ?
The EFCore Find method throws exception because the TEntity is not an entity type but a type deriving from the entity type. So to solve this, we need to first get the most derived type which is the ancestor type of the passed in TEntity type, so when passing in MyStudents you need to get type Students first to use as type argument for Find<> method. Because that type is not known at design time, so we need to use reflection to invoke that Find<> method or better use the other overload of Find that accepts the first argument of entity type (Type). Of course I understand that your Find<> method in your question is from DbContext.Find.
So the solution can be simple like this, firstly we need method to get the most derived entity type from the passed in type (which inherits from the entity type):
public static class DbContextExtensions {
public static Type GetMostDerivedEntityType(this DbContext dbContext, Type type){
while(type != null && dbContext.Model.FindEntityType(type) == null) {
type = type.BaseType;
}
return type;
}
}
Next just use that extension method in your FindNormalized method to find the most derived entity type first before using Find:
//I suppose that this is in the context (class) of your custom DbContext
void FindNormalized<TEntity>(TEntity entity, params object[] keyValues)
where TEntity : class
{
var actualEntityType = this.GetMostDerivedEntityType(typeof(TEntity)) ??
throw new InvalidOperationException($"The type {typeof(TEntity)} is not an entity type or a derive from an entity type");
//use the actualEntityType instead
var res = Find(actualEntityType, keyValues);
if (res == null)
throw new KeyNotFoundException(entity.GetType().Name + " entity key not found " + keyValues[0]);
//copy the properties
CopyPropertiesTo(res, entity);
}
Note that in the above code I use another overload (non-generic version) of Find which accepts the first argument of Type (entity type) directly instead of using your wrapper FindNormalized which is generic only (you can add your one overload of that wrapper which wraps the non-generic Find as used directly in my code above).
I've not tested the code at all. Just try it and let me know if there is any error.
I've taken a look at this answer on how to dynamically create an OrderBy expression in Entity Framework. But I'd like to also build a dynamic Where expression. Something along the lines of this:
public IEnumerable<InventoryItem> GetAll(string filterBy, object value)
{
var results = new List<InventoryItem>();
using (var db = new InventoryDb())
{
if (QueryHelper.PropertyExists<InventoryItem>(filterBy))
{
var query = db.rri_InventoryItems.WhereByProperty(filterBy, value);
foreach(var item in query.Where(expr))
{
results.Add(ConvertItem(item));
}
}
}
return results;
}
Passing in the property to filter by and a value as ab object. Queryable has two methods for Where that both take two parameters, so I am not even sure which is the proper one.
And it's at this point I get a little more lost. I'm not sure how to refactor the original OrderByProerty method to provide a WhereByProperty. I know what I have here is completely wrong. I'm not sure what to do with it.
Ideally, I'd want to extend this even more by providing a collection of objects that could be used to build a query with ands and or operators.
Queryable has two methods for Where that both take two parameters, so I am not even sure which is the proper one.
You need the one that receives Expression<Func<T, bool>> predicate.
Here is how you can build dynamically a predicate similar to (T item) => item.Property == value:
public static partial class QueryableExtensions
{
public static IQueryable<T> WhereEquals<T>(this IQueryable<T> source, string member, object value)
{
var item = Expression.Parameter(typeof(T), "item");
var memberValue = member.Split('.').Aggregate((Expression)item, Expression.PropertyOrField);
var memberType = memberValue.Type;
if (value != null && value.GetType() != memberType)
value = Convert.ChangeType(value, memberType);
var condition = Expression.Equal(memberValue, Expression.Constant(value, memberType));
var predicate = Expression.Lambda<Func<T, bool>>(condition, item);
return source.Where(predicate);
}
}
I've tried to write it in such a way so you can step over the code in order to understand what it does. The only line that might need some explanation is:
var memberValue = member.Split('.').Aggregate((Expression)item, Expression.PropertyOrField);
This is a simple way of handling nested properties like obj.Prop1.Prop2 etc. If you don't need such capability, you can simply use this instead:
var memberValue = Expression.PropertyOrField(item, member);
I didn't need nested properties (yet). I modified your code slightly and have this that is working:
public static IQueryable<T> WhereEquals<T>(
this IQueryable<T> source, string propertyName, object value)
{
if (typeof(T).GetProperty(propertyName, BindingFlags.IgnoreCase |
BindingFlags.Public | BindingFlags.Instance) == null)
{
return null;
}
ParameterExpression parameter = Expression.Parameter(typeof(T), "item");
Expression whereProperty = Expression.Property(parameter, propertyName);
Expression constant = Expression.Constant(value);
Expression condition = Expression.Equal(whereProperty, constant);
Expression<Func<T, bool>> lambda = Expression.Lambda<Func<T, bool>>(condition,parameter);
return source.Where(lambda);
}
If I Add an object to my DbSet like this:
_db.KeywordGroup.Add(keyGroup);
_db.SaveChanges();
The object (keyGroup) get's the Id from the database.
I have a custom Extension I'm using where I try to do the same thing. Basically, I check to see if an object exists in the database. If it does, I would like the existing object returned with it's Id, if not, I want to add the object and get the new Id.
_db.KeywordGroup.AddIfNotExists(keyGroup, true,
k => k.KeywordGroupName == keyGroup.KeywordGroupName);
_db.SaveChanges();
....
public static T AddIfNotExists<T>(this DbSet<T> dbSet,
T entity,
bool returnExists = false,
Expression<Func<T, bool>> predicate = null) where T : class, new()
{
var exists = predicate != null ? dbSet.Where(predicate).FirstOrDefault() : dbSet.FirstOrDefault();
if (exists == null || !returnExists) return exists == null ? dbSet.Add(entity) : null;
entity = exists;
return dbSet.Attach(entity);
}
However, I'm having trouble getting keyGroup to get the Id. How can I get my method to work similar to the default Add function, filling my object with the Id if I find a result.
I have this method in my SurveyController class:
public ActionResult AddProperties(int id, int[] propertyids, int page = 1)
{
var survey = _uow.SurveyRepository.Find(id);
if (propertyids == null)
return GetPropertiesTable(survey, page);
var repo = _uow.PropertySurveyRepository;
propertyids.Select(propertyid => new PropertySurvey
{
//Setting the Property rather than the PropertyID
//prevents the error occurring later
//Property = _uow.PropertyRepository.Find(propertyid),
PropertyID = propertyid,
SurveyID = id
})
.ForEach(x => repo.InsertOrUpdate(x));
_uow.Save();
return GetPropertiesTable(survey, page);
}
The GetPropertiesTable redisplays Properties but PropertySurvey.Property is marked virtual and I have created the entity using the new operator, so a proxy to support lazy loading was never created and it is null when I access it. When we have access direct to the DbContext we can use the Create method to explicitly create the proxy. But I have a unit of work and repository pattern here. I guess I could expose the context.Create method via a repository.Create method and then I need to remember to use that instead of the new operator when I add an entity . But wouldn't it be better to encapsulate the problem in my InsertOrUpdate method? Is there some way to detect that the entity being added is not a proxy when it should be and substitute a proxy? This is my InsertOrUpdate method in my base repository class:
protected virtual void InsertOrUpdate(T e, int id)
{
if (id == default(int))
{
// New entity
context.Set<T>().Add(e);
}
else
{
// Existing entity
context.Entry(e).State = EntityState.Modified;
}
}
Based on the answer supplied by qujck. Here is how you can do it without having to employ automapper:
Edited to always check for proxy - not just during insert - as suggested in comments
Edited again to use a different way of checking whether a proxy was passed in to the method. The reason for changing the technique is that I ran into a problem when I introduced an entity that inherited from another. In that case an inherited entity can fail the entity.e.GetType().Equals(instance.GetType() check even if it is a proxy. I got the new technique from this answer
public virtual T InsertOrUpdate(T e)
{
DbSet<T> dbSet = Context.Set<T>();
DbEntityEntry<T> entry;
if (e.GetType().BaseType != null
&& e.GetType().Namespace == "System.Data.Entity.DynamicProxies")
{
//The entity being added is already a proxy type that supports lazy
//loading - just get the context entry
entry = Context.Entry(e);
}
else
{
//The entity being added has been created using the "new" operator.
//Generate a proxy type to support lazy loading and attach it
T instance = dbSet.Create();
instance.ID = e.ID;
entry = Context.Entry(instance);
dbSet.Attach(instance);
//and set it's values to those of the entity
entry.CurrentValues.SetValues(e);
e = instance;
}
entry.State = e.ID == default(int) ?
EntityState.Added :
EntityState.Modified;
return e;
}
public abstract class ModelBase
{
public int ID { get; set; }
}
I agree with you that this should be handled in one place and the best place to catch all looks to be your repository. You can compare the type of T with an instance created by the context and use something like Automapper to quickly transfer all of the values if the types do not match.
private bool mapCreated = false;
protected virtual void InsertOrUpdate(T e, int id)
{
T instance = context.Set<T>().Create();
if (e.GetType().Equals(instance.GetType()))
instance = e;
else
{
//this bit should really be managed somewhere else
if (!mapCreated)
{
Mapper.CreateMap(e.GetType(), instance.GetType());
mapCreated = true;
}
instance = Mapper.Map(e, instance);
}
if (id == default(int))
context.Set<T>().Add(instance);
else
context.Entry(instance).State = EntityState.Modified;
}
I am using Entity Framework version 4. I need to compare a large (~1 million record) SQL Server table to a longish (~2000) array of complex objects returned from a web service. Five different properties need to be compared to determine whether an instance of the complex object is already in the database.
I created a function that returns an expression for use in .Where and .Any methods. It looks like this (where A is the complex object, and tblA is the EF class):
function Expression<tblA, bool> GetSearchPredicate(A a)
{
return ta => ta.Field1.Equals(a.Field1)
&& ta.Field2.Equals(a.Field2)
&& ta.Field3.Equals(a.Field3)
&& ta.Field4.Equals(a.Field4)
&& ta.Field5.Equals(a.Field5);
}
This works. And I can compare all 2000 instances of A by doing this:
IEnumerable<A> objects = [web service call];
var result = objects.Select(a => !db.tblA.Any(GetSearchPredicate(a)));
That works, too. But it's slow. So I looked into building a utility method that could build an expression that could be transmitted down to the database directly through EF.
I used the code in this question as a basis for building that utility method. The example in that question shows comparing a single property to a series of constants, while my version would have to compare multiple properties to multiple constants. My best effort is below:
public static IQueryable<TEntity> WhereIn<TEntity>
(
this ObjectQuery<TEntity> query,
IEnumerable<Expression<Func<TEntity, bool>>> predicates
)
{
if (predicates == null) throw new ArgumentNullException("predicates");
IEnumerable<ParameterExpression> p = predicates.Select(pred => pred.Parameters.Single()).ToArray();
IEnumerable<Expression> equals = predicates.Select(value =>
(Expression)value.Body);
Expression bigEqual = equals.Aggregate((accumulate, equal) =>
Expression.Or(accumulate, equal));
var result1 = Expression.Lambda<Func<TEntity, bool>>(bigEqual, p.First());
var result = query.Where(result1);
return result;
}
This would be invoked like this:
IEnumerable<A> objects = [web service call];
var result = db.tblA.WhereIn(objects.Select(a => GetSearchPredicate(a)));
What I get is a message saying that "ta" (the placeholder for the TEntity object) is not bound. I thought this was because I had multiple expressions (the variable predicates) being combined, and maybe this message was being thrown because I was only passing the parameter from the first of the predicates IEnumerable. But this happens even if predicates is one expression long.
I am reasonably sure, based on the method I linked to, that I could build an expression comparing each of the five properties to a constant (the values of A.Field1 through A.Field5), rather than passing in the parameter predicates that already has them assembled into a series of expressions. But I would rather not, since that would require my method to know that it's working with types A and tblA, and that's the opposite of generic and general-purpose. (It'd also be complex and messy.)
I hope the examples I've shown explain what I want to do. Can it be done in a generic way?
You will need to replace the parameter in the predicate bodies with a single parameter. Something like this should work:
public static Expression<Func<T, bool>> BuildOr<T>(
IEnumerable<Expression<Func<T, bool>>> predicates)
{
Expression body = null;
ParameterExpression p = null;
Expression<Func<T, bool>> first = null;
foreach (Expression<Func<T, bool>> item in predicates)
{
if (first == null)
{
first = item;
}
else
{
if (body == null)
{
body = first.Body;
p = first.Parameters[0];
}
var toReplace = item.Parameters[0];
var itemBody = ReplacementVisitor.Transform(item, toReplace, p);
body = Expression.OrElse(body, itemBody);
}
}
if (first == null)
{
throw new ArgumentException("Sequence contains no elements.", "predicates");
}
return (body == null) ? first : Expression.Lambda<Func<T, bool>>(body, p);
}
private sealed class ReplacementVisitor : ExpressionVisitor
{
private IList<ParameterExpression> SourceParameters { get; set; }
private Expression ToFind { get; set; }
private Expression ReplaceWith { get; set; }
public static Expression Transform(
LambdaExpression source,
Expression toFind,
Expression replaceWith)
{
var visitor = new ReplacementVisitor
{
SourceParameters = source.Parameters,
ToFind = toFind,
ReplaceWith = replaceWith,
};
return visitor.Visit(source.Body);
}
private Expression ReplaceNode(Expression node)
{
return (node == ToFind) ? ReplaceWith : node;
}
protected override Expression VisitConstant(ConstantExpression node)
{
return ReplaceNode(node);
}
protected override Expression VisitBinary(BinaryExpression node)
{
var result = ReplaceNode(node);
if (result == node) result = base.VisitBinary(node);
return result;
}
protected override Expression VisitParameter(ParameterExpression node)
{
if (SourceParameters.Contains(node)) return ReplaceNode(node);
return SourceParameters.FirstOrDefault(p => p.Name == node.Name) ?? node;
}
}
Your WhereIn method then becomes:
public static IQueryable<TEntity> WhereIn<TEntity>(
this ObjectQuery<TEntity> query,
IEnumerable<Expression<Func<TEntity, bool>>> predicates)
{
if (predicates == null) throw new ArgumentNullException("predicates");
var predicate = BuildOr(predicates);
return query.Where(predicate);
}