I'm trying to create a LINQ method query where a user can input text for search criteria which will search a table column and ignore special characters when looking for the results.
For example: Inputting "ab cd" would result in returning both "ab cd" and "ab, cd".
My LINQ Method is currently the following:
public List<type> GetData(string input)
{
var results = dbContext.table
.Where(s => s.Column.Contains(input))
.ToList();
return results;
}
You can use DbFunctions.Like as of EF 6.2:
public List<type> GetData(string input)
{
var results = dbContext.table
.Where(s => DbFunctions.Like(s.Column, "%"+input.Replace(' ', '%')+"%"))
.ToList();
return results;
}
Related
I am currently implementing a RESTFUL API that provides endpoints to interface with a database .
I want to implement filtering in my API , but I need to provide an endpoint that can provide a way to apply filtering on a table using all the table's columns.
I've found some patterns such as :
GET /api/ressource?param1=value1,param2=value2...paramN=valueN
param1,param2...param N being my table columns and the values.
I've also found another pattern that consists of send a JSON object that represents the query .
To filter on a field, simply add that field and its value to the query :
GET /app/items
{
"items": [
{
"param1": "value1",
"param2": "value",
"param N": "value N"
}
]
}
I'm looking for the best practice to achieve this .
I'm using EF Core with ASP.NET Core for implementing this.
Firstly be cautious about filtering on everything/anything. Base the available filters on what users will need and expand from that depending on demand. Less code to write, less complexity, fewer indexes needed on the DB side, better performance.
That said, the approach I use for pages that have a significant number of filters is to use an enumeration server side where my criteria fields are passed back their enumeration value (number) to provide on the request. So a filter field would comprise of a name, default or applicable values, and an enumeration value to use when passing an entered or selected value back to the search. The requesting code creates a JSON object with the applied filters and Base64's it to send in the request:
I.e.
{
p1: "Jake",
p2: "8"
}
The query string looks like:
.../api/customer/search?filters=XHgde0023GRw....
On the server side I extract the Base64 then parse it as a Dictionary<string,string> to feed to the filter parsing. For example given that the criteria was for searching for a child using name and age:
// this is the search filter keys, these (int) values are passed to the search client for each filter field.
public enum FilterKeys
{
None = 0,
Name,
Age,
ParentName
}
public JsonResult Search(string filters)
{
string filterJson = Encoding.UTF8.GetString(Convert.FromBase64String(filters));
var filterData = JsonConvert.DeserializeObject<Dictionary<string, string>>(filterJson);
using (var context = new TestDbContext())
{
var query = context.Children.AsQueryable();
foreach (var filter in filterData)
query = filterChildren(query, filter.Key, filter.Value);
var results = query.ToList(); //example fetch.
// TODO: Get the results, package up view models, and return...
}
}
private IQueryable<Child> filterChildren(IQueryable<Child> query, string key, string value)
{
var filterKey = parseFilterKey(key);
if (filterKey == FilterKeys.None)
return query;
switch (filterKey)
{
case FilterKeys.Name:
query = query.Where(x => x.Name == value);
break;
case FilterKeys.Age:
DateTime birthDateStart = DateTime.Today.AddYears((int.Parse(value) + 1) * -1);
DateTime birthDateEnd = birthDateStart.AddYears(1);
query = query.Where(x => x.BirthDate <= birthDateEnd && x.BirthDate >= birthDateStart);
break;
}
return query;
}
private FilterKeys parseFilterKey(string key)
{
FilterKeys filterKey = FilterKeys.None;
Enum.TryParse(key.Substring(1), out filterKey);
return filterKey;
}
You can use strings and constants to avoid the enum parsing, however I find enums are readable and keep the sent payload a little more compact. The above is a simplified example and obviously needs error checking. The implementation code for complex filter conditions such as the age to birth date above would better be suited as a separate method, but it should give you some ideas. You can search for children by name, and/or age, and/or parent's name for example.
I have invented and found it useful to combine a few filters into one type for example CommonFilters and make this type parseable from string:
[TypeConverter(typeof(CommonFiltersTypeConverter))]
public class CommonFilters
{
public PageOptions PageOptions { get; set; }
public Range<decimal> Amount { get; set; }
//... other filters
[JsonIgnore]
public bool HasAny => Amount.HasValue || PageOptions!=null;
public static bool TryParse(string str, out CommonFilters result)
{
result = new CommonFilters();
if (string.IsNullOrEmpty(str))
return false;
var parts = str.Split(new[] { ' ', ';' }, StringSplitOptions.RemoveEmptyEntries);
foreach (var part in parts)
{
if (part.StartsWith("amount:") && Range<decimal>.TryParse(part.Substring(7), out Range<decimal> amount))
{
result.Amount = amount;
continue;
}
if (part.StartsWith("page-options:") && PageOptions.TryParse(part.Substring(13), out PageOptions pageOptions))
{
result.PageOptions = pageOptions;
continue;
}
//etc.
}
return result.HasAny;
}
public static implicit operator CommonFilters(string str)
{
if (TryParse(str, out CommonFilters res))
return res;
return null;
}
}
public class CommonFiltersTypeConverter : TypeConverter
{
public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
{
if (sourceType == typeof(string))
{
return true;
}
return base.CanConvertFrom(context, sourceType);
}
public override object ConvertFrom(ITypeDescriptorContext context,
CultureInfo culture, object value)
{
if (value is string str)
{
if (CommonFilters.TryParse(str, out CommonFilters obj))
{
return obj;
}
}
return base.ConvertFrom(context, culture, value);
}
}
the request looks like this:
public class GetOrdersRequest
{
[DefaultValue("page-options:50;amount:0.001-1000;min-qty:10")]
public CommonFilters Filters { get; set; }
//...other stuff
}
In this way you reduce the number of input request parameters, especially when some queries don't care about all filters
If you use swagger map this type as string:
c.MapTypeAsString<CommonFilters>();
public static void MapTypeAsString<T>(this SwaggerGenOptions swaggerGenOptions)
{
swaggerGenOptions.MapType(typeof(T), () => new OpenApiSchema(){Type = "string"});
}
Below find a method that does not work. We fail on the line query.Select(...
Below that find a method with hard coded object property names which does work. But, this method is obviously not dynamic, nor flexible. There may be many properties of a Customer I may wish to search on.
The error string is at bottom. I get it that somehow the LINQ to Entity is unable to deal with conversion of GetValue to some sort of TSQL. Would anyone know of how I might code this up?
public List<Customer> GetForQuery(params Tuple<string, string>[] keyValuePairs) {
using (var db = new DBEntities()) {
var availableProperties = typeof(Customer).GetTypeInfo().DeclaredProperties.ToList();
var query = db.Customers.Select(c => c);
foreach (Tuple<string, string> pair in keyValuePairs) {
PropertyInfo pi = availableProperties.First(p => p.Name.Equals(pair.Item1));
if (pi == null)
continue;
query = query.Where(u => pi.GetValue(u, null).ToString().StartsWith(pair.Item2));
}
var results = query.Select(c => c).ToList();
return results;
}
}
How I might call the above:
CustomerController custController = new CustomerController();
List<Customer> results = custController.GetForQuery(Tuple.Create<string, string>("FName", "Bob" ));
The working fixed method:
public List<Customer> GetForQuery(string firstName = "", string lastName = "", string phoneNumber = "") {
using (var db = new DBEntities()) {
var query = db.Customers.Select(c => c);
if (firstName.HasContent())
query = query.Where(u => u.FName.StartsWith(firstName));
if (lastName.HasContent())
query = query.Where(u => u.LName.StartsWith(lastName));
if (phoneNumber.HasContent())
query = query.Where(u => u.EveningPhone.StartsWith(phoneNumber));
var results = query.Select(c => c).ToList();
return results;
}
}
ERROR:
LINQ to Entities does not recognize the method 'System.Object GetValue(System.Object, System.Object[])' method, and this method cannot be translated into a store expression.
I am using Entity Framework code first and I have code like this:
var foos = context.Foos.Where(f => f.Bar == "Hello World").ToList();
Using an SQL profiler, I see that the script run against the database contained a WHERE statement, as expected.
But when I put the Where predicate in a variable:
Func<Foo, bool> predicate = f => f.Bar == "Hello World");
var foos = context.Foos.Where(predicate).ToList();
the resulting SQL command no longer contains a WHERE statement.
Is there a way that this can work?
Change to Expression<Func<Foo, bool>>
Expression<Func<Foo, bool>> predicate = f => f.Bar == "Hello World";
LinqKit could solve this kind issues. It can be obtained by nuget.
An example about using PredicateBuilder of LinqKit.
IQueryable<Product> SearchProducts (params string[] keywords)
{
var predicate = PredicateBuilder.False<Product>();
foreach (string keyword in keywords)
{
string temp = keyword;
predicate = predicate.Or (p => p.Description.Contains (temp));
}
return dataContext.Products.Where (predicate);
}
How it works
var predicate = PredicateBuilder.True <Product> ();
// is just a shortcut for this:
Expression<Func<Product, bool>> predicate = c => true;
I am implementing a search where I would like to partially match an entity's primary key. For example, if I would search for "123" it would return entities which have primary keys like:
12345
67123
91234
If this were a string, I'd attack it like this:
public PartialViewResult QuickSearch(string searchTerm)
{
var results = db.MyEntities.Where(x => x.myProperty.Contains(searchTerm));
return PartialView("QuickSearch_Results", results);
}
However I'm at a loss on the best way to do this for an int. I'm looking for something like this:
public PartialViewResult QuickSearch(int id)
{
var results = db.MyEntities.Where(x => x.myPropertyId.Contains(int));
return PartialView("QuickSearch_Results", results);
}
But obviously contains is not the right way to go. What would be a correct way of implementing this?
Totally wild and untested guess using the StringConvert method:
public PartialViewResult QuickSearch(int id)
{
string sId = id.ToString();
var results =
from x in db.MyEntities
where SqlFunctions.StringConvert((double)x.myPropertyId)
.Contains(sId)
select x;
return PartialView("QuickSearch_Results", results);
}
db.MyEntities.Where(x => x.myPropertyId.ToString().Contains(id.ToString()));
I Use entity Framework 4.
I would like to be able to create a function that return an Expression func that will be use in a lambda expression.
var ViewModel = _db.Suppliers.Select(model => new {
model,SupType = model.SupplierType.SupplierTypeTexts.Where( st => st.LangID == 1)
});
I would like to make this call like that
var ViewModel = _db.Suppliers.Select(model => new {
model,SupType = model.SupplierType.GetText()
});
My Partial class is:
public partial class SupplierType
{
public Expression<Func<SupplierTypeText, bool>> GetText()
{
return p => p.LangID == 1;
}
How can i perform this.
Easy. For example, Let's assume you have a Product table that is mapped to Products EntitySet in your context, now you want to pass a predicate and select a Product:
Expression<Func<Product, bool>> GetPredicate(int id) {
return (p => p.ProductID == id);
}
You can call GetPredicate() with a Product ID to filter based on that:
var query = ctx.Products.Where(GetPredicate(1)).First();
The point really is that you can always pass a Lambda Expression to where an Expression<T> is needed.
EDIT:
You should change your code like this:
var ViewModel = _db.Suppliers.Select(model => new {
model,
SupType = model.SupplierType.SupplierTypeTexts.Where(GetText())
});
public Expression<Func<SupplierTypeText, bool>> GetText() {
return (stt => stt.LangID == 1);
}
If you want to dynamically create compiled Expression at runtime (as opposed to ones hardcoded against a particular data model at compile time) you need to use the static methods on the Expression class.