[英]Creating dynamic Expression Tree for selected search criteria
I have an Expression Tree
to create a dynamic where clause based on the criteria a user selects on a checkbox. 我有一个Expression Tree
,可以根据用户在复选框上选择的条件来创建动态where子句。
Eg: - User wants to search for: "test" 例如:-用户要搜索:“测试”
User selects 用户选择
1. Prop1 1.属性1
2. Prop2 2. Prop2
for an Object MyDBObject
用于对象MyDBObject
The search query will look like 搜索查询看起来像
dbRecords.Where(r=> r.Prop1.Contains("test") || r.Prop2.Contains("test"))
The reason to use an Expression Tree
is so that it can be used for any unknown number of properties of an unknown object. 使用Expression Tree
的原因是它可以用于未知对象的任意数量的属性。
I almost have it working, but I get Argument Expression is not valid
我几乎可以使用它,但是我得到Argument Expression is not valid
Also how does one initialize an empty boolean expression other than using "something that evaluates to -- true/false" ? 另外,除了使用“评估为-true / false的东西”以外,如何初始化一个空的布尔表达式? I've only read about them for a few hours by now so maybe there's something I didn't see yet. 到目前为止,我只阅读了几个小时,所以也许有些事情我还没有看到。
public static Expression<Func<T, bool>> CreatePredicateFromCrtieriaAndSearchTerm<T>(List<string> checkedCriteria, string searchTerm)
{
// sample checked records
checkedCriteria = new[]
{
new { Name = "Prop1", DisplayValue = "Checkbox value 1" },
new { Name = "Prop2", DisplayValue = "Checkbox value 2" }
}
.Select(x => x.Name).ToList();
var param = Expression.Parameter(typeof(T), "record");
Expression oneEqualsOne = Expression.Equal(Expression.Constant(1), Expression.Constant(1));
// Creates (record => (1=1) AND ...)
Expression<Func<T, bool>> finalExpression = Expression.Lambda<Func<T, bool>>(oneEqualsOne, param);
Console.WriteLine(finalExpression);
try
{
// Iterate through properties, find selected props and create
// (record.SelectedProp1.Contains("searchTerm") || record.SelectedProp2.Contains("searchTerm") ... )
PropertyDescriptorCollection props = TypeDescriptor.GetProperties(typeof(T));
List<Expression> matchExpressions = new List<Expression>();
for (int i = 0; i < props.Count; i++)
{
PropertyDescriptor prop = props[i];
for (int j = 0; j < checkedCriteria.Count; j++)
{
if (prop.Name == checkedCriteria[j])
{
// add to where expression
Expression left = Expression.Property(param, prop.Name);
MethodInfo contains = typeof(string).GetMethod("Contains", new[] { typeof(string) });
Expression right = Expression.Constant(searchTerm, searchTerm.GetType());
Expression matchExpression = Expression.Call(left, contains, right);
matchExpressions.Add(matchExpression);
}
}
}
// Creates (1=0 OR ... OR ...)
Expression currentPredicateBody = Expression.Equal(Expression.Constant(1), Expression.Constant(0));
foreach (var matchExpression in matchExpressions)
{
currentPredicateBody = Expression.MakeBinary(ExpressionType.OrElse, matchExpression, currentPredicateBody);
Console.WriteLine(currentPredicateBody);
}
// ( (1=0) || record.SelectedProp1.Contains("searchTerm") || record.SelectedProp2.Contains("searchTerm") )
if (matchExpressions.Count > 0)
{
oneEqualsOne = Expression.AndAlso(oneEqualsOne, currentPredicateBody);
Console.WriteLine(oneEqualsOne);
}
// Full expression:
// ( record => (1=1) AND ( (1=0) || record.SelectedProp1.Contains("searchTerm") || record.SelectedProp2.Contains("searchTerm") ))
finalExpression = Expression.Lambda<Func<T, bool>>(oneEqualsOne, new ParameterExpression[] { param });
Console.WriteLine(finalExpression);
}
catch (Exception ex)
{
throw new Exception(string.Format(@"Error occurred creating where predicate from checked criteria: {0}", ex.Message));
}
return finalExpression;
}
internal class MyDBObject
{
public int Id { get; set; }
public string Prop1 { get; set; }
public string Prop2 { get; set; }
public string Prop3 { get; set; }
public string Prop4 { get; set; }
public string Prop5 { get; set; }
public string Prop11 { get; set; }
public string Prop12 { get; set; }
public string Prop13 { get; set; }
public string Prop14 { get; set; }
public string Prop15 { get; set; }
public string Prop21 { get; set; }
public string Prop22 { get; set; }
public string Prop23 { get; set; }
public string Prop24 { get; set; }
public string Prop25 { get; set; }
}
public static void Main(string[] args)
{
List<MyDBObject> dbRecords = new List<MyDBObject>
{
new MyDBObject { Id = 1, Prop2 = "O1_P2", Prop3 = "O1_P3", Prop12 = "O1_P12", Prop15 = "O1_P15", Prop24 = "O1_P24", Prop25 = "O1_P25" },
new MyDBObject { Id = 2, Prop15 = "O2_P15", Prop21 = "test", Prop22 = "O2_P22", Prop23 = "O2_P23", Prop24 = "O2_P24", Prop25 = "O2_P25" },
new MyDBObject { Id = 3, Prop21 = "O3_P21", Prop22 = "O3_P22", Prop23 = "O3_P23", Prop24 = "test", Prop25 = "O3_P25" }
};
try
{
var predicate = CreatePredicateFromCrtieriaAndSearchTerm<MyDBObject>(null, "test");
var query = dbRecords.AsQueryable().Provider.CreateQuery<MyObject>(predicate);
List<MyObject> results = query.ToList();
foreach (var rs in results)
{
Console.WriteLine("Id: " + rs.Id);
}
}
catch (Exception ex)
{
Console.WriteLine("Error->> " + ex.Message);
}
}
Try this code: 试试这个代码:
public static Expression<Func<T, bool>> CreatePredicate<T>(List<string> propsToSearch,
string valueToSearch)
{
var parameter = Expression.Parameter(typeof(T), "record");
// filtering is not required
if (!propsToSearch.Any() || string.IsNullOrEmpty(valueToSearch))
return Expression.Lambda<Func<T, bool>>(Expression.Constant(true), parameter);
var props = typeof(T).GetProperties()
.Select(p => p.Name)
.Intersect(propsToSearch.Distinct());
var containsMethod = typeof(string).GetMethod("Contains");
var body = props
.Select(p => Expression.PropertyOrField(parameter, p))
.Aggregate((Expression) Expression.Constant(false),
(c, n) => Expression.OrElse(c,
Expression.Call(n, containsMethod, Expression.Constant(valueToSearch)))
);
var lambda = Expression.Lambda<Func<T, bool>>(body, parameter);
return lambda;
}
It return record => true
if there is no properties to search or search patern is empty. 如果没有要搜索的属性或搜索模式为空,则返回record => true
。 QueryProvider
can be smart enough to not generate sql where
in this case. QueryProvider
足够聪明where
在这种情况下不会生成sql。
Update : I created a demo (it's not working because of security restriction of dotNetFiddle, but localy works fine) 更新 :我创建了一个演示 (由于dotNetFiddle的安全性限制而无法正常工作,但是本地设置可以正常工作)
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