PredicateBuilder

PredicateBuilder provides a concise means of building complex dynamic queries in LInQ.

This implementation was adapted from a blog post by Pete Montgomery.

Use Case

Given an IOT logging data set containing a columns DeviceName, DayOfWeek, and HourOfDay, Select all rows where the device named "Toaster" logged a message during any of an arbitrary set of (day, hour) tuples.

Example

// Create an expression based on the device name
var deviceNameExpression = PredicateBuilder.Create<IotLogEntry>(p => p.DeviceName == "Toaster");

// Create a false expression to initialize the dynamic OR expression
var orExpression = PredicateBuilder.False<IotLogEntry>();

// Add an OR predicate to the expression for each item in the arbitrary set of (day, hour) tuples (queryObjects)
foreach (var queryObject in queryObjects)
{
    orExpression = orExpression.Or(p => p.DayOfWeek == queryObject.DayOfWeek && p.HourOfDay == queryObject.HourOfDay);
}

// Combine the two expressions using AND and materialize the query
var result = dbContext.IotLogEntries.Where(deviceNameExpression.And(orExpression)).ToList();