/// <summary>
/// Constructs an expression that is used to filter entries and execute a search for the specified query
/// on all string type fields of an entity
/// </summary>
/// <param name="searchQuery">The query to be searched for in all string fields</param>
/// <returns>An expression that can be used in queries to the DB context</returns>
///
/// Example:
/// For an entity with string properties `Name` and `Address`, the resulting expression
/// is something like this:
///
/// `x => x.Name.ToLower().Contains(query) || x.Address.ToLower().Contains(query)`
///
internal static Expression <Func <TObject, bool> > ConstructSearchPredicate <TObject>(string searchQuery, params Expression <Func <TObject, string> >[] members)
{
// Create constant with query
var constant = Expression.Constant(searchQuery);
// Input parameter (e.g. "c => ")
var parameter = Expression.Parameter(typeof(TObject), "c");
// Construct expression
Expression finalExpression = null;
foreach (var m in members)
{
// Visit the provided expression and replace the input parameter with the one defined above ("c")
// e.g. (from "x.Something" we get "c.Something")
var memberExpression = new ExpressionParameterVisitor(m.Parameters.First(), parameter)
.VisitAndConvert(m.Body, nameof(ConstructSearchPredicate));
// Get query expression
var partialExpression = GetQueryExpression(memberExpression, constant, memberExpression.Type, CompatiblityMode.Strict);
// Handle case when no OR operation can be constructed
if (finalExpression == null)
{
finalExpression = partialExpression;
}
else
{
finalExpression = Expression.OrElse(finalExpression, partialExpression);
}
}
// Return the constructed expression
return(Expression.Lambda <Func <TObject, bool> >(finalExpression, parameter));
}
/// <summary>
/// Constructs an expression that is used to filter entries and execute a search for the specified query
/// on all string type fields of an entity
/// </summary>
/// <param name="searchQuery">The query to be searched for in all string fields</param>
/// <returns>An expression that can be used in queries to the DB context</returns>
///
/// Example:
/// For an entity with string properties `Name` and `Address`, the resulting expression
/// is something like this:
///
/// `x => x.Name.ToLower().Contains(query) || x.Address.ToLower().Contains(query)`
///
private static Expression <Func <T, bool> > ConstructSearchPredicate <T>(string searchQuery, params Expression <Func <T, string> >[] fields)
{
// Create constant with query
var constant = Expression.Constant(searchQuery);
// Input parameter (e.g. "c => ")
var parameter = Expression.Parameter(typeof(T), "c");
// Find methods that will be run on each property
var containsMethod = typeof(string).GetMethod("Contains", new[] { typeof(string) });
var lowerMethod = typeof(string).GetMethod("ToLowerInvariant", new Type[0]);
// Construct expression
Expression finalBody = null;
foreach (var f in fields)
{
// Visit the provided expression and replace the input parameter with the one defined above ("c")
// e.g. (from "x.Something" we get "c.Something")
var propertyExpression = new ExpressionParameterVisitor(f.Parameters.First(), parameter)
.VisitAndConvert(f.Body, nameof(ConstructSearchPredicate));
// Run lowercase method on property (e.g. "c.<property>.ToLowerInvariant()")
var transformedProperty = Expression.Call(propertyExpression, lowerMethod);
// Run contains on property with provided query (e.g. "c.<property>.ToLowerInvariant().Contains(<query>)")
transformedProperty = Expression.Call(transformedProperty, containsMethod, constant);
// Handle case when no OR operation can be constructed
if (finalBody == null)
{
finalBody = transformedProperty;
}
else
{
finalBody = Expression.Or(finalBody, transformedProperty);
}
}
// Return the constructed expression
return(Expression.Lambda <Func <T, bool> >(finalBody, parameter));
}
