LINQ to SQL - select where text like string array

问题:

I have a List<string> of variable count, and I want to query (via LINQ) a table to find any items that contain any of those strings in the Text column.

Tried this (doesn't work):

items = from dbt in database.Items
         where (stringList.FindAll(s => dbt.Text.Contains(s)).Count > 0)
         select dbt;

Query would be something like:

select * from items where text like '%string1%' or text like '%string2%'

Is this possible?

回答1:

Check this article out to do what you want:
http://www.albahari.com/nutshell/predicatebuilder.aspx

This works like a dream. I essentially cut and pasted their code and got this back (with my own data-scheme of course):

SELECT [t0].[Id], [t0].[DateCreated], [t0].[Name] ...
FROM [dbo].[Companies] AS [t0]
WHERE ([t0].[Name] LIKE @p0) OR ([t0].[Name] LIKE @p1)

Here is the code I ran for the proof of concept:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;

namespace PredicateTest
{
class Program
{
    static void Main(string[] args)
    {
        DataClasses1DataContext dataContext = new DataClasses1DataContext();

        Program p = new Program();
        Program.SearchCompanies("test", "test2");
        var pr = from pi in  dataContext.Companies.Where(Program.SearchCompanies("test", "test2")) select pi;
    }

    DataClasses1DataContext dataContext = new DataClasses1DataContext();

    public static Expression<Func<Company, bool>> SearchCompanies(
                                                  params string[] keywords)
    {
        var predicate = PredicateBuilder.False<Company>();
        foreach (string keyword in keywords)
        {
            string temp = keyword;
            predicate = predicate.Or(p => p.Name.Contains(temp));
        }
        return predicate;
    }

}

public static class PredicateBuilder
{
    public static Expression<Func<T, bool>> True<T>() { return f => true; }
    public static Expression<Func<T, bool>> False<T>() { return f => false; }

    public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1,
                                                        Expression<Func<T, bool>> expr2)
    {
        var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
        return Expression.Lambda<Func<T, bool>>
              (Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters);
    }

    public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1,
                                                         Expression<Func<T, bool>> expr2)
    {
        var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
        return Expression.Lambda<Func<T, bool>>
              (Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters);
    }
}
}

I'd suggest going to the site for the code and explanation.

(I am leaving the first answer because it works well if you need an IN statement)

回答2:

kind of new to the whole LINQ to SQL game, but does this syntax help?

string[] items = new string[] { "a", "b", "c", "d" };

var items = from i in db.Items
             where items.Contains(p.text)
            select i;

Got it from:

http://blog.wekeroad.com/2008/02/27/creating-in-queries-with-linq-to-sql/

回答3:

After reading this post, looking for the same solution as you, I found a solution using the .Any and .All methods for Linq are a nice simple and elegant way to get matching results for arrays.

In this instance I'm using a search input, separated by commas as an example. I don't care if the match is not in the same case.

var qry = Query.Split(',').Select(c => c.Trim().ToLower());

First Get some data to query, from Linq to SQL or wherever

var search = db.tablename;

Using the lambda syntax for nice tight code, and result in matches to .Any string in the query to either the name or description in the table.

search = search.Where(
    record => 
    qry.Any(q => record.Name.ToLower().Contains(q)) || 
    qry.Any(q => record.Description.ToLower().Contains(q)));

If you want only results where all strings are matched within any field you can replace .Any with .All:

search = search.Where(
    record => 
    qry.All(q => record.Name.ToLower().Contains(q)) || 
    qry.All(q => record.Description.ToLower().Contains(q)));

回答4:

Using:

string searh = "test1 test2,test3";    
data.Persons.Search(p => p.Name, search);

Search function is:

public static IQueryable<T> Search<T>(this IQueryable<T> source, Expression<Func<T, string>> selector, string s)
{
    if (string.IsNullOrEmpty(s))
        return source;

    string[] str = s.Split(new char[] { ' ', ',' }, StringSplitOptions.RemoveEmptyEntries);

    MethodInfo methodContains = typeof(string).GetMethod("Contains", new[] { typeof(string) });

    Expression strExpression;
    Expression expressionContains;
    Expression resultExpression = Expression.Empty();

    for (int i = 0; i < str.Length; i++)
    {
        strExpression = Expression.Constant(str[i].Trim(), typeof(string));
        expressionContains = Expression.Call(selector.Body, methodContains, strExpression);

        if (i == 0)
            resultExpression = expressionContains;
        else
            resultExpression = Expression.OrElse(resultExpression, expressionContains);
    }

    Expression<Func<T, bool>> lambdaExpr = Expression.Lambda<Func<T, bool>>(resultExpression, new ParameterExpression[] { selector.Parameters[0] });

    return source.Where(lambdaExpr);
}