Selectize.js with Tags, reload key and value in edit form

This is because <input> while selecting is populated with AdvogadoId and not with Descricao , when you select for example:

Whatyou"see" (gray button with side ox) is actually the label and not the value of <input> , in this case the label uses Descricao and the input uses AdvogadoId see valueField: 'AdvogadoId',

The only way to "practice" what I see doing as you wish would be this and put valueField also as Descricao :

 $("#selectize").each(function () {
    $(this).selectize({
        plugins: ['remove_button'],
        valueField: 'Descricao', //Adicionar descrição aqui também
        labelField: 'Descricao',
        searchField: ['AdvogadoId', 'Descricao'],
        create: false,
        persist: false,
        preload: true,
        initUrl: "/Advogados/PesquisarJson/",
        initData: true,
        load: function (query, callback) {
            $.ajax({
                url: "/Advogados/PesquisarJson/",
                type: 'GET',
                error: function () {
                    callback();
                },
                success: function (res) {
                    callback(res);
                }
            });
        }
    });
});

If you really want to send the ids ( AdvogadoId ) you will have to redo the query on the next page using the ids to bring the descriptions back.

However you may be able to use sessionStorage next to the Selectize.js API to keep the options and add them automatically, an example:

$(function() {
    var target = $("#selectize");
    var keySession = "selectizeData2";

    var update = function(a,b) {
        var opts = this.options;
        setTimeout(function() {//Requer timeout
            var values = target.val().split(",");
            console.log(values);

            var list = [];
            for (var k in opts) {
                current = opts[k];
                if (values.indexOf(current.AdvogadoId) !== -1) {
                    list.push({ AdvogadoId: current.AdvogadoId, Descricao: current.Descricao });
                }
            }

            console.log(JSON.stringify(list));
            sessionStorage.setItem(keySession, JSON.stringify(list));
        }, 1);
    };

    var getTarget = function(selectize) {
        var data = sessionStorage.getItem(keySession);
        var parsedData = JSON.parse(data);
            console.log(parsedData);
        if (parsedData) {
            for (var k in parsedData) {
                var current = parsedData[k];
                selectize.addOption([current]);
                selectize.addItem(current.AdvogadoId);
            }
        }
    };

    target.each(function () {
        var handler = $(this).selectize({
            plugins: ['remove_button'],
            valueField: 'AdvogadoId', //Veja que mantive o ID como value
            labelField: 'Descricao',
            searchField: ['AdvogadoId', 'Descricao'],
            create: false,
            persist: false,
            preload: true,
            initUrl: "test.php",
            initData: true,
            "onItemAdd": update, //Adiciona o evento
            "onItemRemove": update, //Adiciona o evento
            load: function (query, callback) {
                $.ajax({
                    url: "test.php",
                    type: 'GET',
                    error: function () {
                        callback();
                    },
                    success: function (res) {
                        callback(res);
                    }
                });
            }
        });

        getTarget(handler[0].selectize);
    });
});

Following the example of @Felipe can also use a pre-query (although for performance this does not seem good when increasing the number of registered clients), it would be like this (it is necessary to clean the input first because if not the Selectize .js thinks ids already exist):

$(function() {
    var target = $("#selectize");
    var currentValue = target.val();

    target.val("");

    target.each(function () {
        $(this).selectize({
            plugins: ['remove_button'],
            valueField: 'AdvogadoId',
            labelField: 'Descricao',
            searchField: ['AdvogadoId', 'Descricao'],
            create: false,
            persist: false,
            preload: true,
            initUrl: "test.php",
            initData: true,
            onInitialize: function() {
                var self = this;
                var value = "," + currentValue + ",";

                $.ajax({
                  url: "test.php",
                  type: 'GET',
                  success: function(res) {
                    res.forEach(function(existingOption) {
                        self.addOption(existingOption);
                        if (value.indexOf("," + existingOption.AdvogadoId + ",") !== -1) {
                            self.addItem(existingOption.AdvogadoId);
                        }
                    });
                  }
                });
            },
            load: function (query, callback) {
                $.ajax({
                    url: "test.php",
                    type: 'GET',
                    error: function () {
                        callback();
                    },
                    success: function (res) {
                        callback(res);
                    }
                });
            }
        });
    });
});

To solve this problem you will need to make a fix using the onInitialize method. The solution is not pretty, but it solves this library deficiency:

$(this).selectize({
  plugins: ['remove_button'],
  valueField: 'Sigla',
  labelField: 'Nome',
  searchField: ['Sigla', 'Nome'],
  create: false,
  persist: false,
  preload: true,
  initUrl: "/Advogados/PesquisarJson/",
  initData: true,
  load: function(query, callback) {
    $.ajax({
      url: "/Advogados/PesquisarJson/",
      type: 'GET',
      error: function() {
        callback();
      },
      success: function(res) {
        callback(res);
      }
    });
  },
  // Bugfix
  onInitialize: function() {

    var self = this;
    var value = self.getValue();

    $.ajax({
      url: "/Advogados/PesquisarJson/",
      type: 'GET',
      success: function(res) {

        res.forEach(function(existingOption) {
          self.addOption(existingOption);
          self.addItem(existingOption[self.settings.valueField]);
        });

        self.setValue(value);
        self.blur();
      }
    });

  }
});