动态linq表达式

本文关键字：表达式 linq 动态 | 更新日期: 2023-09-27 18:18:27

我有一个Linq应用程序，我需要得到一个动态的where表达式。我使用class:

public class EntityColumnsField
{
    public String ColumnName { get; set; }
    public Type ColumnType { get; set; }
    public bool IsPK { get; set; }
    public String TableName { get; set; }
    public Type TableType { get; set; }
}

我得到列表的列实体的方法:

public static IEnumerable<EntityColumnsField> GetAllColumnsFromEntity(params EntityObject[] entities)
    {
        if (entities == null || entities.Count() == 0)
            throw new ArgumentNullException("entity");
        List<EntityColumnsField> ColumnList = new List<EntityColumnsField>();
        foreach (var entity in entities)
        {
            ColumnList.AddRange(from p in entity.GetType().GetProperties()
                                where p.GetCustomAttributes(typeof(EdmScalarPropertyAttribute), false).Any()
                                select new EntityColumnsField()
                                {
                                    TableName = entity.GetType().Name,
                                    ColumnName = p.Name,
                                    ColumnType = p.PropertyType,
                                    IsPK = p.GetCustomAttributes(false).Where(a => a is EdmScalarPropertyAttribute && ((EdmScalarPropertyAttribute)a).EntityKeyProperty).Count() > 0
                                });
        }
        return ColumnList.OrderBy(a => a.TableName);
    }

我有3个表(用户，UserPartner和UserFriends)，我需要生成所有字符串字段的条件。我试着这样做:

using (var db = new DB())
            {
                var ll = from x in db.Users 
                         join y in db.UserPartners on x.ID equals y.ID
                         join z in db.UserFriends on x.ID equals z.ID
                         select new { Users = x, UserPartners = y, UserFriends = z };
            }
if (!String.IsNullOrEmpty(fulltext))
{
var AllSearchField = Utils.GetAllColumnsFromEntity(new User(), new UserPartner(), new UserFriends());
//TODO:
//Here i need a code, which generate predicate for all text fields in tables
//the result would be like :
//ll.Where(a => a.Users.Address.Contains(fulltext) || a.Users.Email.Contains(fulltext) || a.UserPartners.Email.Contains(m.FullText))
}

有谁知道怎么做吗?由于

动态linq表达式

你可以试试Dynamic Linq

NuGet:https://www.nuget.org/packages/System.Linq.Dynamic

ScottGu示例:http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

试试这种方法: 

System.Linq.Dynamic 1.0.0

这是.Net 4.0 Dynamic language功能的Microsoft程序集。

安装System.Linq.Dynamic，在Package Manager Console

中运行以下命令
PM> Install-Package System.Linq.Dynamic

你可能需要这样的东西，

var ll;
using (var db = new DB())
{
    ll = from x in db.Users 
             join y in db.UserPartners on x.ID equals y.ID
             join z in db.UserFriends on x.ID equals z.ID
             select new { Users = x, UserPartners = y, UserFriends = z };
}
if (!String.IsNullOrEmpty(fulltext))
{
    var AllSearchField = Utils.GetAllColumnsFromEntity(new User(), new UserPartner(), new UserFriends());
    //TODO:
    //Here i need a code, which generate predicate for all text fields in tables
    //the result would be like :
    foreach (var source in ll.Where(a => a.Users.Address.Contains(fulltext) || a.Users.Email.Contains(fulltext) || a.UserPartners.Email.Contains(m.FullText)))
    {
        // do something with source    
    }
}

你也可以使用FindAll函数

foreach (var source in ll.FindAll(a => a.Users.Address.Contains(fulltext) || a.Users.Email.Contains(fulltext) || a.UserPartners.Email.Contains(m.FullText)))
    {
        // do something with source    
    }
相关文章：