Web Api function in CRM 2016 C#

This is webapi C# 

  public class EntityRepository : Repository where T : Crmbaseentity
    {
        public async Task Add(T entity, string EntityName)
        {
            using (HttpClient client = new HttpClient(new HttpClientHandler() { Credentials = new NetworkCredential(this.UserName, this.Password, this.Domain) }))
            {
                HttpResponseMessage response = await HttpClientExtensions.SendAsJsonAsync(client, HttpMethod.Post, this.CrmHost + EntityName, entity);

                if (response.IsSuccessStatusCode)
                    return true;
                else
                    return false;

            }
        }

        public async Task Get(string EntityGuid, string EntityName)
        {
            T item = null;
            using (var client = new HttpClient(new HttpClientHandler() { Credentials = new NetworkCredential(this.UserName, this.Password, this.Domain) }))
            {
                client.BaseAddress = new Uri(this.CrmHost);
                client.DefaultRequestHeaders.Accept.Clear();
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                client.DefaultRequestHeaders.Add("OData-MaxVersion", "4.0");
                client.DefaultRequestHeaders.Add("OData-Version", "4.0");

                HttpResponseMessage response = await client.GetAsync(EntityName + "(" + EntityGuid + ")");

                if (response.IsSuccessStatusCode)
                {
                    var Content = await response.Content.ReadAsStringAsync();
                    T itemres = JsonConvert.DeserializeObject(Content);
                    item = itemres;
                }
                else
                {

                }
            }

            return item;
        }

        public async Task> FilterbyContains(string EntityName,string property,string value)
        {
            List list = new List();
            using (var client = new HttpClient(new HttpClientHandler() { Credentials = new NetworkCredential(this.UserName, this.Password, this.Domain) }))
            {
                client.BaseAddress = new Uri(this.CrmHost);
                client.DefaultRequestHeaders.Accept.Clear();
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                client.DefaultRequestHeaders.Add("OData-MaxVersion", "4.0");
                client.DefaultRequestHeaders.Add("OData-Version", "4.0");

                HttpResponseMessage response = await client.GetAsync(EntityName + string.Format("?$filter=contains({0},\'{1}\')", property,value));

                if (response.IsSuccessStatusCode)
                {
                    var Content = await response.Content.ReadAsStringAsync();
                    ODataResponse itemres = JsonConvert.DeserializeObject>(Content);
                    list = this.CollectionFromResponseSet(itemres.Value);
                }
                else
                {

                }
            }

            return list;
        }

        public async Task> GetAll(string EntityName)
        {
            List list = new List();

            using (var client = new HttpClient(new HttpClientHandler() { Credentials = new NetworkCredential(this.UserName, this.Password, this.Domain) }))
            {
                
                client.BaseAddress = new Uri(this.CrmHost);
                client.DefaultRequestHeaders.Accept.Clear();
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                client.DefaultRequestHeaders.Add("OData-MaxVersion", "4.0");
                client.DefaultRequestHeaders.Add("OData-Version", "4.0");

                HttpResponseMessage retrieveResponse = await client.GetAsync(EntityName);

                if (retrieveResponse.IsSuccessStatusCode)
                {
                    var Content = await retrieveResponse.Content.ReadAsStringAsync();
                    ODataResponse  odataresponse = JsonConvert.DeserializeObject>(Content);
                    list = this.CollectionFromResponseSet(odataresponse.Value);
                }
                else
                {

                }
            }

            return list;
        }


        public async Task Update(T entity, string EntityName, string EntityId)
        {
            using (HttpClient client = new HttpClient(new HttpClientHandler() { Credentials = new NetworkCredential(this.UserName, this.Password, this.Domain) }))
            {

                HttpResponseMessage response = await HttpClientExtensions.SendAsJsonAsync(client, new HttpMethod("PATCH"), this.CrmHost + EntityName + "(" + EntityId + ")", entity);

                if (response.IsSuccessStatusCode)
                    return true;
                else
                    return false;
            }
        }

        public async Task Delete(string EntityName, string EntityId)
        {
            using (HttpClient client = new HttpClient(new HttpClientHandler() { Credentials = new NetworkCredential(this.UserName, this.Password, this.Domain) }))
            {

                HttpResponseMessage response = await client.DeleteAsync(this.CrmHost + EntityName + "(" + EntityId + ")");

                if (response.IsSuccessStatusCode)
                    return true;
                else
                    return false;
            }
        }
    }