如何对包含EntityFunctions.AddDays函数的GetNewValues()进行单元测试

Question

下面的示例代码在生产中工作正常,但由于EntityFunctions无法进行单元测试.

我的单元测试项目使用InMemoryDatabase而不是真正的SQL数据库.我可以通过使用计算列myValue和newValue在SQL数据库中创建View来轻松解决我的问题.我喜欢找到一种方法来进行单元测试工作,而无需更改我的方法,也无需创建新的SQL视图

---

public class EcaseReferralCaseRepository : Repository
{

        public class myType
        {
                public DateTime myValue;
                public DateTime newValue;
        }

        public myType GetNewValues()
        {
                return 
                        (myType)(from o in context.EcaseReferralCases
                        select new myType
                        {
                            // LINQ to Entity
                            myValue = (DateTime)System.Data.Objects.EntityFunctions.AddDays(o.StartDate, 0),
                            newValue = (DateTime)System.Data.Objects.EntityFunctions.AddDays(o.StartDate, 30)

                            // LINQ to Object
                            //myValue = o.StartDate.AddDays(0),
                            //newValue = o.StartDate.AddDays(30)

                        });
        }
}

---

这个链接显示了单元测试EntityFunctions的一个很好的例子,我用这种方法解决了我的单元测试难度之一,但不知道如何解决这个问题.

Answer 1

除非我弄错了,否则你要将EcaseReferralCases的实现切换为另一个IQueryable,可能是LINQ To Objects可查询源.

最强大的方法可能是使用表达式访问者将调用替换为EntityFunctions您自己的L2Objects兼容函数.

这是我的实现:

using System;
using System.Data.Objects;
using System.Linq;
using System.Linq.Expressions;

static class EntityFunctionsFake
{
    public static DateTime? AddDays(DateTime? original, int? numberOfDays)
    {
        if (!original.HasValue || !numberOfDays.HasValue)
        {
            return null;
        }
        return original.Value.AddDays(numberOfDays.Value);
    }
}
public class EntityFunctionsFakerVisitor : ExpressionVisitor
{
    protected override Expression VisitMethodCall(MethodCallExpression node)
    {
        if (node.Method.DeclaringType == typeof(EntityFunctions))
        {
            var visitedArguments = Visit(node.Arguments).ToArray();
            return Expression.Call(typeof(EntityFunctionsFake), node.Method.Name, node.Method.GetGenericArguments(), visitedArguments);
        }

        return base.VisitMethodCall(node);
    }
}
class VisitedQueryProvider<TVisitor> : IQueryProvider
    where TVisitor : ExpressionVisitor, new()
{
    private readonly IQueryProvider _underlyingQueryProvider;
    public VisitedQueryProvider(IQueryProvider underlyingQueryProvider)
    {
        if (underlyingQueryProvider == null) throw new ArgumentNullException();
        _underlyingQueryProvider = underlyingQueryProvider;
    }

    private static Expression Visit(Expression expression)
    {
        return new TVisitor().Visit(expression);
    }

    public IQueryable<TElement> CreateQuery<TElement>(Expression expression)
    {
        return new VisitedQueryable<TElement, TVisitor>(_underlyingQueryProvider.CreateQuery<TElement>(Visit(expression)));
    }

    public IQueryable CreateQuery(Expression expression)
    {
        var sourceQueryable = _underlyingQueryProvider.CreateQuery(Visit(expression));
        var visitedQueryableType = typeof(VisitedQueryable<,>).MakeGenericType(
            sourceQueryable.ElementType,
            typeof(TVisitor)
            );

        return (IQueryable)Activator.CreateInstance(visitedQueryableType, sourceQueryable);
    }

    public TResult Execute<TResult>(Expression expression)
    {
        return _underlyingQueryProvider.Execute<TResult>(Visit(expression));
    }

    public object Execute(Expression expression)
    {
        return _underlyingQueryProvider.Execute(Visit(expression));
    }
}
public class VisitedQueryable<T, TExpressionVisitor> : IOrderedQueryable<T>
    where TExpressionVisitor : ExpressionVisitor, new()
{
    private readonly IQueryable<T> _underlyingQuery;
    private readonly VisitedQueryProvider<TExpressionVisitor> _queryProviderWrapper;
    public VisitedQueryable(IQueryable<T> underlyingQuery)
    {
        _underlyingQuery = underlyingQuery;
        _queryProviderWrapper = new VisitedQueryProvider<TExpressionVisitor>(underlyingQuery.Provider);
    }

    public IEnumerator<T> GetEnumerator()
    {
        return _underlyingQuery.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }

    public Expression Expression
    {
        get { return _underlyingQuery.Expression; }
    }

    public Type ElementType
    {
        get { return _underlyingQuery.ElementType; }
    }

    public IQueryProvider Provider
    {
        get { return _queryProviderWrapper; }
    }
}

这是一个用法示例:

var linq2ObjectsSource = new List<DateTime?>() { null }.AsQueryable();
var visitedSource = new VisitedQueryable<DateTime?, EntityFunctionsFakerVisitor>(linq2ObjectsSource);
var visitedQuery = visitedSource.Select(dt => EntityFunctions.AddDays(dt, 1));
var results = visitedQuery.ToList();
Assert.AreEqual(1, results.Count);
Assert.AreEqual(null, results[0]);

通过这种方式,您可以获得所有理想的特征:

• 开发人员可以继续使用EntityFunctionsEntity Framework定义的标准;
• 如果没有在数据库上运行,生产实现仍然可以保证引发异常;
• 可以针对虚假存储库测试查询;