Including standard functions in search criteria

OData protocol supports standard functions that can be included in search criteria.

Find a product with the given name coverted to a lowercase format:
Request URI: Products?$filter=tolower(ProductName)+eq+%27chai%27

var product = _db.Products.Find(_db.Products.ProductName.ToLower() == "chai");
Assert.Equal("Chai", product.ProductName);

Find a product with the length of name equal to 4:
Request URI: Products?$filter=length(ProductName)+eq+4

var product = _db.Products.Find(_db.Products.ProductName.Length() == 4);
Assert.NotEmpty(products);

Find a product with the name starting with the given string:
Request URI: Products?$filter=startswith(ProductName%2c%27Ch%27)+eq+true

var product = _db.Products.Find(_db.Products.ProductName.StartsWith("Ch") == true);
Assert.NotEmpty(products);

Find a product with the name containing the given string:
Request URI: Products?$filter=substringof(%27ai%27%2cProductName)+eq+true

var product = _db.Products.Find(_db.Products.ProductName.Contains("ai") == true);
Assert.NotEmpty(products);

Find a product with the name not containing the given string:
Request URI: Products?$filter=substringof(%27ai%27%2cProductName)+eq+false

var product = _db.Products.Find(_db.Products.ProductName.Contains("ai") == false);
Assert.NotEmpty(products);

Find a product with the name containing the given string at the specified position:
Request URI: Products?$filter=indexof(ProductName%2c%27ai%27)+eq+2

var product = _db.Products.Find(_db.Products.ProductName.IndexOf("ai") == 2);
Assert.NotEmpty(products);

Alternative syntax for finding a product with the name containing the given string at the specified position:
Request URI: Products?$filter=substring(ProductName%2c1)+eq+%27hai%27

var product = _db.Products.Find(_db.Products.ProductName.Substring(1) == "hai");
Assert.NotEmpty(products);

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See also:
OData URI conventions