sqlite examples

.gitignore

@@ -87,4 +87,6 @@ python/examples/pytest/coverage/.coverage
 crystal/bin
 crystal/lib
 crystal/counter.yaml
+crystal/counter.json
+crystal/counter.db
 

crystal/README.md

@@ -11,7 +11,6 @@
 * Classes
 
 
-* Read YAML file in general
 * Read shard.yml file in particular
 * Web application development?
 * Access to SQLite?

crystal/examples/files/multi_counter_yaml.cr

@@ -22,7 +22,3 @@ else
         puts "#{i}: #{arg}"
     }
 end
-
-
-
-

crystal/examples/multi_counter_sqlite.cr

@@ -0,0 +1,36 @@
+require "sqlite3"
+
+db_file = "counter.db"
+if ! File.exists?(db_file)
+    DB.open "sqlite3://#{db_file}" do |db|
+        db.exec "CREATE TABLE counters (name TEXT, count INTEGER, UNIQUE(name))"
+    end
+end
+
+DB.open "sqlite3://#{db_file}" do |db|
+    if ARGV.size == 1
+        name = ARGV[0]
+        count = 0
+        db.query "SELECT count FROM counters WHERE name=?", name do |rs|
+            rs.each do
+                count = rs.read(Int32)
+            end
+        end
+
+        count += 1
+        puts count
+
+        if count == 1
+            db.exec "INSERT INTO counters VALUES (?, ?)", name, count
+        else
+            db.exec "UPDATE counters SET count=? WHERE name=?", count, name
+        end       
+    else
+        db.query "SELECT name, count FROM counters ORDER BY name DESC" do |rs|
+            puts "#{rs.column_name(0)} (#{rs.column_name(1)})"
+            rs.each do
+              puts "#{rs.read(String)} (#{rs.read(Int32)})"
+            end
+        end
+    end
+end

crystal/examples/try_sqlite.cr

@@ -0,0 +1,36 @@
+require "sqlite3"
+
+# You need to install the development package for libsqlite3
+# On Ubuntu
+# sudo apt-get install libsqlite3-dev
+
+
+# Based on the example in the documentation
+db_file = "data.db"
+if File.exists?(db_file)
+    puts "File #{db_file} already exists. Aborting"
+    exit(1)
+end
+DB.open "sqlite3://#{db_file}" do |db|
+  db.exec "CREATE TABLE contacts (name TEXT, age INTEGER)"
+  db.exec "INSERT INTO contacts VALUES (?, ?)", "John Doe", 30
+
+  args = [] of DB::Any
+  args << "Sarah"
+  args << 33
+  db.exec "INSERT INTO contacts VALUES (?, ?)", args: args
+
+  puts "max age:"
+  puts db.scalar "SELECT max(age) FROM contacts" # => 33
+
+  puts "contacts:"
+  db.query "SELECT name, age FROM contacts ORDER BY age DESC" do |rs|
+    puts "#{rs.column_name(0)} (#{rs.column_name(1)})"
+    # => name (age)
+    rs.each do
+      puts "#{rs.read(String)} (#{rs.read(Int32)})"
+      # => Sarah (33)
+      # => John Doe (30)
+    end
+  end
+end

crystal/examples/use_yaml.cr

@@ -4,4 +4,14 @@ data = File.open("examples/crystal.yml") do |file|
     YAML.parse(file)
 end
 puts data
-puts data["language"]
+puts typeof(data) # YAML::Any
+puts data["language"]
+puts data["language"]["first_year"]
+puts typeof(data["language"]["first_year"].to_s.to_i)
+# [YAML::Any](https://crystal-lang.org/api/YAML/Any.html)
+puts data.as_h.keys
+data.as_h.keys.each {|main_key|
+    data[main_key].as_h.keys.each {|sub_key|
+        puts data[main_key][sub_key]
+    }
+}

crystal/files.md

@@ -91,4 +91,6 @@
 {i: from_yaml}
 {i: to_yaml}
 
+* [YAML](https://crystal-lang.org/api/YAML.html)
+
 ![](examples/files/multi_counter_yaml.cr)

crystal/other.md

@@ -162,7 +162,19 @@ shards install
 {id: yaml}
 {i: YAML}
 
+* [YAML](https://crystal-lang.org/api/YAML.html)
+
 ![](examples/crystal.yml)
 ![](examples/use_yaml.cr)
 
+## SQLite
+{id: sqlite}
+{i: SQLite}
+
+![](examples/try_sqlite.cr)
+
+## Multi-counter with SQLite
+{id: multi-counter-sqlite}
+{i: SQLite}
 
+![](examples/multi_counter_sqlite.cr)

crystal/shard.lock

@@ -4,3 +4,11 @@ shards:
     git: https://github.com/crystal-ameba/ameba.git
     version: 0.14.3
 
+  db:
+    git: https://github.com/crystal-lang/crystal-db.git
+    version: 0.10.1
+
+  sqlite3:
+    git: https://github.com/crystal-lang/crystal-sqlite3.git
+    version: 0.18.0
+

crystal/shard.yml

@@ -10,6 +10,8 @@ description: |
 dependencies:
   ameba:
     github: crystal-ameba/ameba
+  sqlite3:
+    github: crystal-lang/crystal-sqlite3
 
 
 #development_dependencies: