Add and remove fields from Solr schema using Schema API...

Okay - I know what you're thinking. "How can I quickly update my Solr schema without having to go into the schema config file - perhaps using a rest API?" You can use the Solr Schema API, that's how! 

I recently noticed that there is a Schema API in Solr 5.X that can be used to update the Solr schema. You need to have the schemaFactory set to use the "ManagedIndexSchemaFactory", and have the mutable property set to true.  If you want to stop allowing the schema from being updated via the API, then you can change the mutable property to false.

Here are a few of the things that you can do with the schema API:

View the schema for a collection:

http://localhost:8983/solr/yourcollectionname/schema

View all of the fields in the schema:

http://localhost:8983/solr/yourcollectionname/schema/fields

Example output:

{
  "responseHeader":{
    "status":0,
    "QTime":101
  },
  "fields":[
  {
      "name":"_text_",
      "type":"text_general",
      "multiValued":true,
      "indexed":true,
      "stored":false},
    {
      "name":"_version_",
      "type":"long",
      "indexed":true,
      "stored":true},
    {
      "name":"id",
      "type":"string",
      "multiValued":false,
      "indexed":true,
      "required":true,
      "stored":true,
      "uniqueKey":true},
    {
      "name":"somefieldname",
      "type":"lowercase",
      "indexed":true,
      "stored":true},
    {
      "name":"title",
      "type":"strings"
    }
  ]
}


View a specific field in the schema:

http://localhost:8983/solr/yourcollectionname/schema/fields/somefieldname

Example output:

{
  "responseHeader":{
    "status":0,
    "QTime":1},
  "field":{
    "name":"somefieldname",
    "type":"lowercase",
    "indexed":false,
    "stored":true
  }
}

Now add a new field called "anotherfield" that is of type "text_en", stored, and indexed:

curl -X POST -H 'Content-type:application/json' --data-binary '{"add-field":{"name":"anotherfield","type":"text_en","stored":true,"indexed":true }}' http://localhost:8983/solr/yourcollectionname/schema


Now let's see that the field exists:

http://localhost:8983/solr/yourcollectionname/schema/fields/anotherfield

{
  "responseHeader":
  {
    "status":0,
    "QTime":1
  },
  "field":
  {
    "name":"anotherfield",
    "type":"text_en",
    "indexed":true,
    "stored":true
    }
}

Now let's delete the field:

curl -X POST -H 'Content-type:application/json' --data-binary '{"delete-field" : { "name":"anotherfield" }}' http://localhost:8983/solr/yourcollectionname/schema

And check to see that it is deleted:

http://localhost:8983/solr/yourcollectionname/schema/fields/anotherfield

{
  "responseHeader":
  {
    "status":404,
    "QTime":2
  },
  "error":
  {
    "msg":"Field 'anotherfield' not found.",
    "code":404
  }
}

There are other actions that you can do using the Schema API. Here are a few of the things that you can do using the Schema API:
- replace a field
- add and remove dynamic field patterns
- view dynamic fields
- and and remove field types
- view field types