A flexible generic IRepository interface you can use on both the front end and back end. You can use it on the back end to access data, and also on the client to define a generic API Repository, which wraps calls to the API with an HttpClient object.
Nuget: https://www.nuget.org/packages/AvnRepository/
APIEntityResponse.cs
public class APIEntityResponse<TEntity> where TEntity : class
{
public bool Success { get; set; }
public List<string> ErrorMessages { get; set; } = new List<string>();
public TEntity Data { get; set; }
}APIListOfEntityResponse.cs
public class APIListOfEntityResponse<TEntity> where TEntity : class
{
public bool Success { get; set; }
public List<string> ErrorMessages { get; set; } = new List<string>();
public IEnumerable<TEntity> Data { get; set; }
}These two classes will be used as return types for our API controllers to add a little context to the actual entities returned.
IRepository.cs
using Microsoft.EntityFrameworkCore;
using System.Linq.Expressions;
using System.Reflection;
#nullable disable
/// <summary>
/// Generic repository interface that uses
/// </summary>
/// <typeparam name="TEntity"></typeparam>
public interface IRepository<TEntity> where TEntity : class
{
Task<bool> DeleteAsync(TEntity EntityToDelete);
Task<bool> DeleteByIdAsync(object Id);
Task DeleteAllAsync(); // Be Careful!!!
Task<IEnumerable<TEntity>> GetAsync(QueryFilter<TEntity> Filter);
Task<IEnumerable<TEntity>> GetAllAsync();
Task<TEntity> GetByIdAsync(object Id);
Task<TEntity> InsertAsync(TEntity Entity);
Task<TEntity> UpdateAsync(TEntity EntityToUpdate);
}The IRepository<TEntity> interface will be used on the server as well as the client to ensure compatibility accessing data, no matter where the code resides.
This class file also includes code to describe custom queries that can easily be sent and received as JSON.
QueryFilter.cs
/// <summary>
/// A serializable filter. An alternative to trying to serialize and deserialize LINQ expressions,
/// which are very finicky. This class uses standard types.
/// </summary>
/// <typeparam name="TEntity"></typeparam>
public class QueryFilter<TEntity> where TEntity : class
{
/// <summary>
/// If you want to return a subset of the properties, you can specify only
/// the properties that you want to retrieve in the SELECT clause.
/// Leave empty to return all columns
/// </summary>
public List<string> IncludePropertyNames { get; set; } = new List<string>();
/// <summary>
/// Defines the property names and values in the WHERE clause
/// </summary>
public List<FilterProperty> FilterProperties { get; set; } = new List<FilterProperty>();
/// <summary>
/// Specify the property to ORDER BY, if any
/// </summary>
public string OrderByPropertyName { get; set; } = "";
/// <summary>
/// Set to true if you want to order DESCENDING
/// </summary>
public bool OrderByDescending { get; set; } = false;
/// <summary>
/// A custome query that returns a list of entities with the current filter settings.
/// </summary>
/// <param name="AllItems"></param>
/// <returns></returns>
public async Task<IEnumerable<TEntity>> GetFilteredListAsync(List<TEntity> AllItems)
{
// Convert to IQueryable
var query = AllItems.AsQueryable<TEntity>();
// the expression will be used for each FilterProperty
Expression<Func<TEntity, bool>> expression = null;
// Process each property
foreach (var filterProperty in FilterProperties)
{
// use reflection to get the property info
PropertyInfo prop = typeof(TEntity).GetProperty(filterProperty.Name);
// string
if (prop.PropertyType == typeof(string))
{
if (filterProperty.Operator == FilterOperator.Equals)
if (filterProperty.CaseSensitive == false)
expression = s => s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString().ToLower() == filterProperty.Value.ToString().ToLower();
else
expression = s => s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString() == filterProperty.Value.ToString();
else if (filterProperty.Operator == FilterOperator.NotEquals)
if (filterProperty.CaseSensitive == false)
expression = s => s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString().ToLower() != filterProperty.Value.ToString().ToLower();
else
expression = s => s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString() != filterProperty.Value.ToString();
else if (filterProperty.Operator == FilterOperator.StartsWith)
if (filterProperty.CaseSensitive == false)
expression = s => s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString().ToLower().StartsWith(filterProperty.Value.ToString().ToLower());
else
expression = s => s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString().StartsWith(filterProperty.Value.ToString());
else if (filterProperty.Operator == FilterOperator.EndsWith)
if (filterProperty.CaseSensitive == false)
expression = s => s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString().ToLower().EndsWith(filterProperty.Value.ToString().ToLower());
else
expression = s => s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString().EndsWith(filterProperty.Value.ToString());
else if (filterProperty.Operator == FilterOperator.Contains)
if (filterProperty.CaseSensitive == false)
expression = s => s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString().ToLower().Contains(filterProperty.Value.ToString().ToLower());
else
expression = s => s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString().Contains(filterProperty.Value.ToString());
}
// int
if (prop.PropertyType == typeof(int))
{
int value = Convert.ToInt32(filterProperty.Value);
if (filterProperty.Operator == FilterOperator.Equals)
expression = s => Convert.ToInt32(s.GetType().GetProperty(filterProperty.Name).GetValue(s)) == value;
else if (filterProperty.Operator == FilterOperator.NotEquals)
expression = s => Convert.ToInt32(s.GetType().GetProperty(filterProperty.Name).GetValue(s)) != value;
else if (filterProperty.Operator == FilterOperator.LessThan)
expression = s => Convert.ToInt32(s.GetType().GetProperty(filterProperty.Name).GetValue(s)) < value;
else if (filterProperty.Operator == FilterOperator.GreaterThan)
expression = s => Convert.ToInt32(s.GetType().GetProperty(filterProperty.Name).GetValue(s)) > value;
else if (filterProperty.Operator == FilterOperator.LessThanOrEqual)
expression = s => Convert.ToInt32(s.GetType().GetProperty(filterProperty.Name).GetValue(s)) <= value;
else if (filterProperty.Operator == FilterOperator.GreaterThanOrEqual)
expression = s => Convert.ToInt32(s.GetType().GetProperty(filterProperty.Name).GetValue(s)) >= value;
}
// datetime
if (prop.PropertyType == typeof(DateTime))
{
DateTime value = DateTime.Parse(filterProperty.Value);
if (filterProperty.Operator == FilterOperator.Equals)
expression = s => DateTime.Parse(s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString()) == value;
else if (filterProperty.Operator == FilterOperator.NotEquals)
expression = s => DateTime.Parse(s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString()) != value;
else if (filterProperty.Operator == FilterOperator.LessThan)
expression = s => DateTime.Parse(s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString()) < value;
else if (filterProperty.Operator == FilterOperator.GreaterThan)
expression = s => DateTime.Parse(s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString()) > value;
else if (filterProperty.Operator == FilterOperator.LessThanOrEqual)
expression = s => DateTime.Parse(s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString()) <= value;
else if (filterProperty.Operator == FilterOperator.GreaterThanOrEqual)
expression = s => DateTime.Parse(s.GetType().GetProperty(filterProperty.Name).GetValue(s).ToString()) >= value;
}
// Add expression creation code for other data types here.
// apply the expression
query = query.Where(expression);
}
// Include the specified properties
foreach (var includeProperty in IncludePropertyNames)
{
query = query.Include(includeProperty);
}
// order by
if (OrderByPropertyName != "")
{
PropertyInfo prop = typeof(TEntity).GetProperty(OrderByPropertyName);
if (prop != null)
{
if (OrderByDescending)
query = query.Where(expression).OrderByDescending(x => prop.GetValue(x, null));
else
query = query.Where(expression).OrderBy(x => prop.GetValue(x, null));
}
}
// execute and return the list
return query.ToList();
}
}The QueryFilter<TEntity> can be used on the client as well as the server to define the same level of filter as using LINQ, except that it easily travels across the wire.
IncludedPropertyNamesdefines the columns to return, ala the SELECT clauseFilterPropertiesdefines the properties to compare, ala the WHERE clauseOrderByPropertyNamedefines the sort column, ala the ORDER BY clauseOrderByDescendingdefines the direction of the sort, ala DESC- The
GetFilteredListmethod applies the current filter settings given a list of all items. While it's true that all of the items need to be loaded, what you give up in memory efficiency you gain in convenience. This method currently handles properties of typestring,int32andDateTime.
FilterProperty.cs
/// <summary>
/// Defines a property for the WHERE clause
/// </summary>
public class FilterProperty
{
public string Name { get; set; } = "";
public string Value { get; set; } = "";
public FilterOperator Operator { get; set; }
public bool CaseSensitive { get; set; } = false;
}The FilterProperty class defines columns to compare:
Nameis the Name of the propertyValueis a string representation of the value of the propertyCaseSensitiveis a flag to determine whether case-sensitivity should be appliedFilterOeratordefines how to compare the column values (StartsWith, etc.)
FilterOperator.cs
/// <summary>
/// Specify the compare operator
/// </summary>
public enum FilterOperator
{
Equals,
NotEquals,
StartsWith,
EndsWith,
Contains,
LessThan,
GreaterThan,
LessThanOrEqual,
GreaterThanOrEqual
}I've created a demo that uses AvnRepository to create back end repositories for in-memory data, Entity Framework, and Dapper at https://github.com/carlfranklin/BlazorRepositoryDemo