这应该会有所帮助。但是,您将不得不具体化 Anonymous 类型才能使其正常工作。Expression<Func<Anonymous, Person>>
我的 LinqPropertyChain 无法使用它,因为它仍然是匿名的,很难创建。
Expression<Func<Person, object>> orderBy = x => x.Name;
using(var dbContext = new MyDbContext())
{
var keyword = "term";
var startsWithResults = dbContext.People
.Where(x => x.Name.StartsWith(keyword))
.Select(x => new {
Rank = 1,
Entity = x,
});
var containsResults = dbContext.People
.Where(x => !startsWithResults.Select(y => y.Entity.Id).Contains(x.Id))
.Where(x => x.Name.Contains(keyword))
.Select(x => new {
Rank = 2,
Entity = x,
});
var rankedResults = startsWithResults.Concat(containsResults)
.OrderBy(x => x.Rank)
.ThenBy(LinqPropertyChain.Chain(x => x.Entity, orderBy));
// TODO: apply thenby ordering here based on the orderBy expression above
}
public static class LinqPropertyChain
{
public static Expression<Func<TInput, TOutput>> Chain<TInput, TOutput, TIntermediate>(
Expression<Func<TInput, TIntermediate>> outter,
Expression<Func<TIntermediate, TOutput>> inner
)
{
Console.WriteLine(inner);
Console.WriteLine(outter);
var visitor = new Visitor(new Dictionary<ParameterExpression, Expression>
{
{inner.Parameters[0], outter.Body}
});
var newBody = visitor.Visit(inner.Body);
Console.WriteLine(newBody);
return Expression.Lambda<Func<TInput, TOutput>>(newBody, outter.Parameters);
}
private class Visitor : ExpressionVisitor
{
private readonly Dictionary<ParameterExpression, Expression> _replacement;
public Visitor(Dictionary<ParameterExpression, Expression> replacement)
{
_replacement = replacement;
}
protected override Expression VisitParameter(ParameterExpression node)
{
if (_replacement.ContainsKey(node))
return _replacement[node];
else
{
return node;
}
}
}
}
想出了一种用更少的显式泛型来做到这一点的方法。
Expression<Func<Person, object>> orderBy = x => x.Name;
Expression<Func<Foo, Person>> personExpression = x => x.Person;
var helper = new ExpressionChain(personExpression);
var chained = helper.Chain(orderBy).Expression;
// Define other methods and classes here
public class ExpressionChain<TInput, TOutput>
{
private readonly Expression<Func<TInput, TOutput>> _expression;
public ExpressionChain(Expression<Func<TInput, TOutput>> expression)
{
_expression = expression;
}
public Expression<Func<TInput, TOutput>> Expression { get { return _expression; } }
public ExpressionChain<TInput, TChained> Chain<TChained>
(Expression<Func<TOutput, TChained>> chainedExpression)
{
var visitor = new Visitor(new Dictionary<ParameterExpression, Expression>
{
{_expression.Parameters[0], chainedExpression.Body}
});
var lambda = Expression.Lambda<Func<TInput, TOutput>>(newBody, outter.Parameters);
return new ExpressionChain(lambda);
}
private class Visitor : ExpressionVisitor
{
private readonly Dictionary<ParameterExpression, Expression> _replacement;
public Visitor(Dictionary<ParameterExpression, Expression> replacement)
{
_replacement = replacement;
}
protected override Expression VisitParameter(ParameterExpression node)
{
if (_replacement.ContainsKey(node))
return _replacement[node];
else
{
return node;
}
}
}
}