有没有一种方法可以在linq查询中参数化方法? [英] Is there a way to parameterize method in a linq query?

问题描述

在使用Linq to SQL的应用程序中，用户可以搜索文本.搜索表达式的开头和/或结尾可以使用星号(*).现在的代码是这样的:

In my application with Linq to SQL, the user can search for text. An asterix (*) can be used at the beginning and/or end of the search expression. The code now is this:

var search = SearchTextBox.Text.Trim();
bool filterStartsWith = false, filterEndsWith = false;
if (!string.IsNullOrEmpty(search))
{
    filterStartsWith = search.EndsWith("*");
    filterEndsWith = search.StartsWith("*");
    if (filterStartsWith) search = search.Substring(0, search.Length - 1);
    if (filterEndsWith) search = search.Substring(1);

    if (filterStartsWith)
    {
        if (filterEndsWith)
        {
            query = query.Where(item => item.Omschrijving.Contains(search));
        }
        else
        {
            query = query.Where(item => item.Omschrijving.StartsWith(search));
        }
    }
    else
    {
        if (filterEndsWith)
        {
            query = query.Where(item => item.Omschrijving.EndsWith(search));
        }
        else
        {
            query = query.Where(item => item.Omschrijving == search);
        }
    }
}

但是，我想对此进行概括，因为这种搜索发生在更多的地方.另外，对于某些表，这应该在多个列上发生.有任何想法吗?

However, I want to generalize this, because this kind of search happens on more places. Also, some tables, this should happen on more than one column. Any ideas?

我将Visual Studio 2010与.NET Framework 4.0一起使用.

I use Visual Studio 2010 with .NET Framework 4.0.

推荐答案

您可以尝试以下方法:

static IQueryable<T> WhereColumnContains<T>(this IQueryable<T> source, Expression<Func<T, string>> selector, string search)
{
    if (string.IsNullOrWhiteSpace(search))
    {
        return source;
    }

    Expression<Func<T, bool>> expression;

    search = search.Trim();

    var filterStartsWith = search.EndsWith("*");
    var filterEndsWith = search.StartsWith("*");

    if (filterEndsWith) search = search.Substring(1);

    if (filterStartsWith)
    {
        search = search.Substring(0, search.Length - 1);

        if (filterEndsWith)
        {
            var parameter = Expression.Parameter(typeof(T), "parameter");

            expression = Expression.Lambda<Func<T, bool>>(
                Expression.Call(Expression.Invoke(selector, parameter), typeof(string).GetMethod("Contains", new[] { typeof(string) }), Expression.Constant(search)),
                parameter);
        }
        else
        {
            var parameter = Expression.Parameter(typeof(T), "parameter");

            expression = Expression.Lambda<Func<T, bool>>(
                Expression.Call(Expression.Invoke(selector, parameter), typeof(string).GetMethod("StartsWith", new[] { typeof(string) }), Expression.Constant(search)),
                parameter);
        }
    }
    else
    {
        if (filterEndsWith)
        {
            var parameter = Expression.Parameter(typeof(T), "parameter");

            expression = Expression.Lambda<Func<T, bool>>(
                Expression.Call(Expression.Invoke(selector, parameter), typeof(string).GetMethod("EndsWith", new[] { typeof(string) }), Expression.Constant(search)),
                parameter);
        }
        else
        {
            var parameter = Expression.Parameter(typeof(T), "parameter");

            expression = Expression.Lambda<Func<T, bool>>(
                Expression.Equal(Expression.Invoke(selector, parameter), Expression.Constant(search)),
                parameter);
        }
    }

    return source.Where(expression);
}

按以下方式调用它:

query = query.WhereColumnContains(item => item.Omschrijving, search);

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