LINQ PredicateBuilder 在我的动态搜索中不起作用

Question

我的数据库中有一本书 table，我的 edmx 中有一个名为 vwShared 的图书视图。我想使用运算符创建动态搜索供用户查找书籍。我有 2 个 SearchColumns 下拉列表包含 "Title, Authors, Published Year, Subject"。我有 2 个 SearchType 下拉列表包含 "StartsWith, Contains, EndsWith, Equals"。我有另一个下拉列表包含 "AND, OR" 以组合 2 个搜索结果。以下是我的代码。

var predicate = PredicateBuilder.True<DataLayer.vwShared>();

if (joinOperator == "AND")
{
if (SearchColumn1 == "Title" && SearchType1 == "Contains")
predicate = predicate.And(e1 => e1.Title.Contains(txtSearch1.Text));
if (SearchColumn2 == "Authors" && SearchType2 == "Contains")
predicate = predicate.And(e1 => e1.Authors.Contains(txtSearch2.Text));
}
else if (joinOperator == "OR")
{
if (SearchColumn1 == "Title" && SearchType1 == "Contains")
predicate = predicate.Or(e1 => e1.Title.Contains(txtSearch1.Text));
if (SearchColumn2 == "Authors" && SearchType2 == "Contains")
predicate = predicate.Or(e1 => e1.Authors.Contains(txtSearch2.Text));
}

List<DataLayer.vwShared> bookList= new DataLayer.Solib_DMREntities().SP_SharedData_GetAll("AllLocal").ToList<DataLayer.vwShared>();

var bookList= from books in bookList.AsQueryable().Where(predicate)
                select books ;

gvBooks.DataSource = bookList.ToList();
gvBooks.DataBind();

以上代码不是 return 正确的结果。有什么不对。？以下是我的参考网站。 http://www.albahari.com/nutshell/predicatebuilder.aspx 请多多指教

谢谢。

Answer 1

步1:Model

public class Person
{
    public int PersonId { get; set; }
    public int? Age { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int? Salary { get; set; }

}


public class PersonDBContext : DbContext
{
    public virtual DbSet<Person> People { get; set; }
}

第 2 步：控制器

public class PersonController
{

    PersonDBContext db = new PersonDBContext();

    public void Add(Person person)
    {
        db.People.Add(person);
        db.SaveChanges();
    }
    public List<Person> GetAll()
    {
        return db.People.ToList();
    }

    public List<Person> GetByPredicateValue(Expression<Func<Person, bool>> predicate)
    {
        if (predicate != null)
            return db.People.Where(predicate.Compile()).ToList();
        else
            return null;
    }

    public List<Person> GetByPredicateAndPersonListValue(List<Person> PeopleList,Expression<Func<Person, bool>> predicate)
    {
        if (predicate != null)
            return PeopleList.Where(predicate.Compile()).ToList();
        else
            return null;
    }


}

第 3 步：隐藏代码

public partial class MainWindow : Window
    {
        PersonController pc;
        public static List<Person> PeopleFilterList = null;
        public static string CurrentColumn = null;
        public MainWindow()
        {

            pc = new PersonController();        
            InitializeComponent();
            grid.ItemsSource = pc.GetAll();
            grid.PreviewMouseDown += grid_PreviewMouseDown;
        }

        void grid_PreviewMouseDown(object sender, MouseButtonEventArgs e)
        {
            TableViewHitInfo hi = ((TableView)grid.View).CalcHitInfo(e.OriginalSource as DependencyObject);
            if (hi == null) return;
            if (hi.HitTest == TableViewHitTest.ColumnHeader || hi.HitTest == TableViewHitTest.ColumnHeaderFilterButton)
            {
                grid.UnselectAll();
                GridColumn currentColumn = ((DevExpress.Xpf.Grid.GridViewHitInfoBase)(hi)).Column;
                CurrentColumn = currentColumn.FieldName;
                (grid.View as TableView).SelectCells(0, currentColumn, grid.VisibleRowCount - 1, currentColumn);            
            }
        }

        Expression<Func<Person, bool>> _result=null;
        string str="";
        private void IdForm_ButtonClicked(object sender, IdentityUpdateEventArgs e)
        {
            _result = e.FirstName;
        }

        public MainWindow(Expression<Func<Person, bool>> result)
        {
            Window1 f = new Window1();
            f.IdentityUpdated += new Window1.IdentityUpdateHandler(IdForm_ButtonClicked);
            pc = new PersonController();
            InitializeComponent();                 
            _result = result;
            if (PeopleFilterList != null)
                PeopleFilterList = pc.GetByPredicateAndPersonListValue(PeopleFilterList,_result).ToList();
            else
                PeopleFilterList = pc.GetByPredicateValue(_result).ToList();
            grid.ItemsSource = PeopleFilterList;
            grid.PreviewMouseDown += grid_PreviewMouseDown;
        }


        private void Button_Click(object sender, RoutedEventArgs e)
        {
            Window1 w1 = new Window1(CurrentColumn);
            w1.Show();

        }

    }

第 4 步：过滤后面的代码

 public partial class Window1 : Window
    {
        public delegate void IdentityUpdateHandler(object sender, IdentityUpdateEventArgs e);
        public event IdentityUpdateHandler IdentityUpdated;


        string _currentColumn = null;
        public Window1()
        {
            InitializeComponent();
        }

        public Window1(string currentColumn)
        {
            _currentColumn = currentColumn;
            InitializeComponent();
        }

        public static Expression<Func<Person, bool>> predicateValue;
        IdentityUpdateEventArgs args;
        private void Button_Click(object sender, RoutedEventArgs e)
        {

            string operatorName = "";


            if (!String.IsNullOrEmpty(txtSmaller.Text.Trim()))
                operatorName = txtSmaller.Name;
            else if (!String.IsNullOrEmpty(txtElder.Text.Trim()))
                operatorName = txtElder.Name;
            else if (!String.IsNullOrEmpty(txtContains.Text.Trim()))
                operatorName = txtContains.Name;
            else if (!String.IsNullOrEmpty(txtStartWith.Text.Trim()))
                operatorName = txtStartWith.Name;
            else if (!String.IsNullOrEmpty(txtEqual.Text.Trim()))
                operatorName = txtEqual.Name;
            else if (!String.IsNullOrEmpty(txtNotEqual.Text.Trim()))
                operatorName = txtNotEqual.Name;
            else if (!String.IsNullOrEmpty(txtSmallerOrEqual.Text.Trim()))
                operatorName = txtSmallerOrEqual.Name;
            else if (!String.IsNullOrEmpty(txtElderOrEqual.Text.Trim()))
                operatorName = txtElderOrEqual.Name;

            else if (!String.IsNullOrEmpty(txtSmallerThan.Text.Trim()) && !String.IsNullOrEmpty(txtBiggerThan.Text.Trim()))
                operatorName = txtSmallerThan.Name;


            switch (operatorName)
            {
                case "txtSmaller":          
                    predicateValue = (x => (int)x.GetType().GetProperty(_currentColumn).GetValue(x, null) < Convert.ToInt32(txtSmaller.Text));
                    break;

                case "txtElder":
                    predicateValue = (x => (int)x.GetType().GetProperty(_currentColumn).GetValue(x, null) > Convert.ToInt32(txtElder.Text));
                    break;

                case "txtSmallerOrEqual":
                    predicateValue = (x => (int)x.GetType().GetProperty(_currentColumn).GetValue(x, null) <= Convert.ToInt32(txtSmallerOrEqual.Text));
                    break;

                case "txtElderOrEqual":
                    predicateValue = (x => (int)x.GetType().GetProperty(_currentColumn).GetValue(x, null) >= Convert.ToInt32(txtElderOrEqual.Text));
                    break;

                case "txtEqual":
                    predicateValue = (x => (int)x.GetType().GetProperty(_currentColumn).GetValue(x, null) == Convert.ToInt32(txtEqual.Text));
                    break;

                case "txtNotEqual":
                    predicateValue = (x => (int)x.GetType().GetProperty(_currentColumn).GetValue(x, null) != Convert.ToInt32(txtNotEqual.Text));
                    break;

                case "txtSmallerThan":
                    predicateValue = (x => (int)x.GetType().GetProperty(_currentColumn).GetValue(x, null) >= Convert.ToInt32(txtBiggerThan.Text)
                    && (int)x.GetType().GetProperty(_currentColumn).GetValue(x, null) <= Convert.ToInt32(txtSmallerThan.Text));
                    break;

                case "txtStartWith":
                    predicateValue = (x => x.GetType().GetProperty(_currentColumn).GetValue(x, null).ToString().StartsWith(txtStartWith.Text));      
                    break;

                case "txtContains":
                    predicateValue = (x => x.GetType().GetProperty(_currentColumn).GetValue(x,null).ToString().Contains(txtContains.Text));                    
                    break;                  
            }




            MainWindow mw = new MainWindow(predicateValue);
            mw.Show();
            this.Close();
        }

        void Window1_IdentityUpdated(object sender, IdentityUpdateEventArgs e)
        {
            e = args;
        }

    }

    public class IdentityUpdateEventArgs : System.EventArgs
    {
        private Expression<Func<Person, bool>> mFirstName;

        public IdentityUpdateEventArgs(Expression<Func<Person, bool>> sFirstName)
        {
            this.mFirstName = sFirstName;
        }

        public Expression<Func<Person, bool>> FirstName
        {
            get
            {
                return mFirstName;
            }
        }    

    }

Answer 2

回答你的具体问题。问题出在构建OR predicate 的分支，在这种情况下你应该从PredicateBuilder.False 开始，否则根本不会过滤（我们从学校知道，true or something 是总是 true :)

// ...
else if (joinOperator == "OR")
{
    predicate = PredicateBuilder.False<DataLayer.vwShared>();
    // ...
}
// ...

LINQ PredicateBuilder 在我的动态搜索中不起作用

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