Before I forget it, my execution context, I'm using .Net 5 with the packages:
- Microsoft.EntityFrameworkCore.Design 5.0.6
- Microsoft.EntityFrameworkCore.Relational 5.0.6
- MySql.EntityFrameworkCore 5.0.3.1
My main goal was to remove the repetitive task of doing expressions when I need to retrieve entities, something like:
public class GetListEntity
{
property int QueryProperty { get; set }
}
public class Entity
{
property int Property { get; set }
}
public async Task<ActionResult> List(GetListEntity getListEntity)
{
var restrictions = new List<Expression<Func<Entity>
if (model.QueryProperty != null)
{
restrictions.Add(e => e.Property == model.QueryProperty);
}
... //Add all the queryable properties and Aggregate the Expression on the variable expectedEntity and get an IQueryable of the entities as queryableEntities from my DbContext
var nonTrackedQueryableEntities = queryableEntities.Where(expectedEntity)
.AsNoTracking();
// I will get the total first because the API was meant to paginate the responses.
var total = await entites.CountAsync();
}
I've managed to achieve what I wanted but let's say... partially, because if I try to Query the Database at least two times in a row I get this exception:
System.ArgumentException: An item with the same key has already been added. Key: e
at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.CompareLambda(LambdaExpression a, LambdaExpression b)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.Compare(Expression left, Expression right)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.Compare(Expression left, Expression right)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.CompareBinary(BinaryExpression a, BinaryExpression b)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.Compare(Expression left, Expression right)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.CompareLambda(LambdaExpression a, LambdaExpression b)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.Compare(Expression left, Expression right)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.CompareUnary(UnaryExpression a, UnaryExpression b)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.Compare(Expression left, Expression right)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.CompareExpressionList(IReadOnlyList`1 a, IReadOnlyList`1 b)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.CompareMethodCall(MethodCallExpression a, MethodCallExpression b)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.Compare(Expression left, Expression right)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.CompareExpressionList(IReadOnlyList`1 a, IReadOnlyList`1 b)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.CompareMethodCall(MethodCallExpression a, MethodCallExpression b)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.Compare(Expression left, Expression right)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.CompareExpressionList(IReadOnlyList`1 a, IReadOnlyList`1 b)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.CompareMethodCall(MethodCallExpression a, MethodCallExpression b)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.ExpressionComparer.Compare(Expression left, Expression right)
at Microsoft.EntityFrameworkCore.Query.ExpressionEqualityComparer.Equals(Expression x, Expression y)
at Microsoft.EntityFrameworkCore.Query.CompiledQueryCacheKeyGenerator.CompiledQueryCacheKey.Equals(CompiledQueryCacheKey other)
at Microsoft.EntityFrameworkCore.Query.RelationalCompiledQueryCacheKeyGenerator.RelationalCompiledQueryCacheKey.Equals(RelationalCompiledQueryCacheKey other)
at MySql.EntityFrameworkCore.Query.Internal.MySQLCompiledQueryCacheKeyGenerator.MySQLCompiledQueryCacheKey.Equals(MySQLCompiledQueryCacheKey other)
at MySql.EntityFrameworkCore.Query.Internal.MySQLCompiledQueryCacheKeyGenerator.MySQLCompiledQueryCacheKey.Equals(Object obj)
at System.Collections.Concurrent.ConcurrentDictionary`2.TryGetValue(TKey key, TValue& value)
at Microsoft.Extensions.Caching.Memory.MemoryCache.TryGetValue(Object key, Object& result)
at Microsoft.Extensions.Caching.Memory.CacheExtensions.TryGetValue[TItem](IMemoryCache cache, Object key, TItem& value)
at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler)
at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.ExecuteAsync[TResult](Expression query, CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.ExecuteAsync[TResult](Expression expression, CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ExecuteAsync[TSource,TResult](MethodInfo operatorMethodInfo, IQueryable`1 source, Expression expression, CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ExecuteAsync[TSource,TResult](MethodInfo operatorMethodInfo, IQueryable`1 source, CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.CountAsync[TSource](IQueryable`1 source, CancellationToken cancellationToken)'
Following the trace I managed to discover that the ORM is caching for some reason my expressions (and putting the parameter name, in this case 'e') and failing to detect a key collision the second time it has a similar expression to query the database. I said for some reason because, it's not the main deal but at least is odd that cache is involved in a non tracked query, maybe I'm missing something in the middle.
To undenrstand how i got here i will put the code below.
First an interface to implement in every model related with querying a list of entities and expose the extension method ListRestrictions (almost at the bottom).
public interface IEntityFilter<TEntity>
{
}
The next step was to define Attributes to summarize the action to do with the property and generate a partial expression to use in the extension method:
[AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
public abstract class FilterByPropertyAttribute : Attribute
{
protected string FirstPropertyPath { get; }
protected IEnumerable<string> NPropertyPath { get; }
public FilterByPropertyAttribute(string firstPropertyPath, params string[] nPropertyPath)
{
this.FirstPropertyPath = firstPropertyPath;
this.NPropertyPath = nPropertyPath;
}
protected MemberExpression GetPropertyExpression(ParameterExpression parameterExpression)
{
var propertyExpression = Expression.Property(parameterExpression, this.FirstPropertyPath);
foreach (var propertyPath in this.NPropertyPath)
{
propertyExpression = Expression.Property(propertyExpression, propertyPath);
}
return propertyExpression;
}
And to avoid comparisons with nullable structs
public abstract Expression GetExpression(ParameterExpression parameterExpression, object propertyValue);
}
public abstract class NonNullableValuePropertyFilterAttribute : FilterByPropertyAttribute
{
public NonNullableValuePropertyFilterAttribute(string firstPropertyPath, params string[] nPropertyPath)
: base(firstPropertyPath, nPropertyPath)
{
}
public override Expression GetExpression(ParameterExpression parameterExpression, object propertyValue)
{
var propertyExpression = this.GetPropertyExpression(parameterExpression);
return this.GetExpression(propertyExpression, this.GetConvertedConstantExpression(propertyExpression, Expression.Constant(propertyValue)));
}
protected abstract Expression GetExpression(MemberExpression memberExpression, UnaryExpression unaryExpression);
private UnaryExpression GetConvertedConstantExpression(MemberExpression memberExpression, ConstantExpression constantExpression)
{
var convertedConstantExpression = Expression.Convert(constantExpression, memberExpression.Type);
return convertedConstantExpression;
}
}
An Attribute with a defined role would be:
public class EqualPropertyFilterAttribute : NonNullableValuePropertyFilterAttribute
{
public EqualPropertyFilterAttribute(string firstPropertyPath, params string[] nPropertyPath)
: base(firstPropertyPath, nPropertyPath)
{
}
protected override Expression GetExpression(MemberExpression memberExpression, UnaryExpression unaryExpression)
{
return Expression.Equal(memberExpression, unaryExpression);
}
}
And last, the extension itself:
public static class EntityFilterExtensions
{
public static List<Expression<Func<TEntity, bool>>> ListRestrictions<TEntity>(this IEntityFilter<TEntity> entityFilter)
{
var entityFilterType = entityFilter.GetType();
var propertiesInfo = entityFilterType.GetProperties()
.Where(pi => pi.GetValue(entityFilter) != null
&& pi.CustomAttributes.Any(ca => ca.AttributeType
.IsSubclassOf(typeof(FilterByPropertyAttribute))));
var expressions = Enumerable.Empty<Expression<Func<TEntity, bool>>>();
if (propertiesInfo.Any())
{
var entityType = typeof(TEntity);
var parameterExpression = Expression.Parameter(entityType, "e");
expressions = propertiesInfo.Select(pi =>
{
var filterByPropertyAttribute = Attribute.GetCustomAttribute(pi, typeof(FilterByPropertyAttribute)) as FilterByPropertyAttribute;
var propertyValue = pi.GetValue(entityFilter);
var expression = filterByPropertyAttribute.GetExpression(parameterExpression, propertyValue);
return Expression.Lambda<Func<TEntity, bool>>(expression, parameterExpression);
});
}
return expressions.ToList();
}
}
A usage would be:
public class GetListEntity : IEntityFilter<Entity>
{
[EqualPropertyFilter(nameof(Entity.Property))]
property int QueryProperty { get; set }
}
public class Entity
{
property int Property { get; set }
}
public async Task<ActionResult> List(GetListEntity getListEntity)
{
var restrictions = getListEntity.ListRestrictions();
... //Add all the queryable properties and Aggregate the Expression on the variable expectedEntity and get an IQueryable of the entities as queryableEntities from my DbContext
var nonTrackedQueryableEntities = queryableEntities.Where(expectedEntity)
.AsNoTracking();
// I will get the total first because the API was meant to paginate the responses.
var total = await entites.CountAsync();
}
And to be discarded, if I Aggregate a non dynamic expression of a list of expressions, the ORM works fine, when I do it with the dynamic ones I get the exception at the beginning.
I found a workaround, changing in the method extension this line:
var parameterExpression = Expression.Parameter(entityType, "e");
For this one:
var parameterExpression = Expression.Parameter(entityType, $"{entityType.Name}{entityFilter.GetHashCode()}");
I wanna know why this happens and maybe if there is another way to fix it. I posted here before opening a thread in any Github repository because I'm still curious if is a fault of mine for missing something in the way or a bug.
