LinQ 查询 - 动态添加 Where

Question

我很难解决这个问题，需要在 C#、asp.net 中创建动态 linq 查询的代码。我有 5 个下拉列表，用于搜索同一数据库表中的不同列并将项目过滤值返回到单个列表框。问题是在 DDL 中没有选择 which 或 all 或 any 的顺序，但组合过滤结果应显示在列表框中。我有一个有效的查询，它分别为每个 DDL 选择分别搜索并返回一列中的结果。必须使用 AND 添加 where 子句才能将其他 DDL 选择动态添加到此查询中。谢谢

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public ListItemCollection searchProject(ListItemCollection projList, String searchstr, String columnName)
{
    DataSet DSToReturn = new DataSet();

    ListItemCollection returnItems = new ListItemCollection();
    DataTable results = (from d in ((DataSet)_MyDataset).Tables["Records"].AsEnumerable()
                         orderby d.Field<string>("Name") ascending
                         where (d.Field<string>(columnName) != null)
                         where d[columnName].ToString().ToLower().Contains(searchstr.ToLower())
                         select d).CopyToDataTable();

    foreach (ListItem li in projList)
    {
        if ((from System.Data.DataRow row in results.Rows
             where li.Value.Equals(row["value"].ToString(), StringComparison.InvariantCultureIgnoreCase)
             select row["value"]).Count() > 0)
        returnItems.Add(li);
    }

    return returnItems;
}

Answer 1

这里有一些示例代码说明我们如何做到这一点...

    private void DataPortal_Fetch(GoalCriteria criteria)
    {
        using (var ctx = ContextManager<Data.ExodusDataContext>
                    .GetManager(Database.ApplicationConnection, false))
        {
            this.RaiseListChangedEvents = false;
            this.IsReadOnly = false;

            // set option to eager load child object(s)
            var opts = new System.Data.Linq.DataLoadOptions();
            opts.LoadWith<Data.Goal>(row => row.Contact);
            opts.LoadWith<Data.Goal>(row => row.Sales);
            opts.LoadWith<Data.Goal>(row => row.Customer);
            ctx.DataContext.LoadOptions = opts;

            IQueryable<Data.Goal> query = ctx.DataContext.Goals;

            if (criteria.Name != null) // Name
                query = query.Where(row => row.Name.Contains(criteria.Name));

            if (criteria.SalesId != null) // SalesId
                query = query.Where(row => row.SalesId == criteria.SalesId);

            if (criteria.Status != null) // Status
                query = query.Where(row => row.Status == (int)criteria.Status);

            if (criteria.Statuses.Count != 0) // Statuses
                query = query.Where(row => criteria.Statuses.Contains((GoalStatus)row.Status));

            if (criteria.ContactId != null) // ContactId
                query = query.Where(row => row.ContactId == criteria.ContactId);

            if (criteria.CustomerId != null) // CustomerId
                query = query.Where(row => row.CustomerId == criteria.CustomerId);

            if (criteria.ScheduledDate.DateFrom != DateTime.MinValue) // ScheduledDate
                query = query.Where(t => t.ScheduledDate >= criteria.ScheduledDate.DateFrom);
            if (criteria.ScheduledDate.DateTo != DateTime.MaxValue)
                query = query.Where(t => t.ScheduledDate <= criteria.ScheduledDate.DateTo);

            if (criteria.CompletedDate.DateFrom != DateTime.MinValue) // ComplatedDate
                query = query.Where(t => t.CompletedDate >= criteria.CompletedDate.DateFrom);
            if (criteria.CompletedDate.DateTo != DateTime.MaxValue)
                query = query.Where(t => t.CompletedDate <= criteria.CompletedDate.DateTo);

            if (criteria.MaximumRecords != null) // MaximumRecords
                query = query.Take(criteria.MaximumRecords.Value);

            var data = query.Select(row => GoalInfo.FetchGoalInfo(row));

            this.AddRange(data);

            this.IsReadOnly = true;
            this.RaiseListChangedEvents = true;
        }
    }

我们只检查分配给我们的条件对象的空值，如果它不为空，那么我们将其附加到查询中。